Posted on

Cannabis seeds in a rock womb

Alcohol & Other Drugs

Everywhere you turn today, it seems somebody is talking about cannabis.

Some of the information we hear about cannabis is conflicting, making it hard to understand the ways it may affect our children. Is it addictive? Does it cause psychosis? Is it really a medicine? What will happen if my child uses it? What should I tell—or not tell—my child about it?

As cannabis has now been legalized for adults in Canada, the Canadian Institute for Substance Use Research has revised and updated a previous resource developed in partnership with the F.O.R.C.E. Society for Kids’ Mental Health and the Canadian Mental Health Association (BC Division). This new edition retains the aim of the earlier work.

Our goal is to offer you an honest and thoughtful discussion on cannabis so you can make better decisions about cannabis use—or non-use—in the context of your family.

Hemp. Cannabis. Marijuana. Hash.

Chances are you’ve heard these words before, though you many not know the difference between them. Are they the same or different? The answer is “both.”

HEMP is a plant that, like other plants, has roots, a stalk, leaves, flowers and seeds. Hemp stalks are often used to make fibre-based items such as paper and fabric.

CANNABIS is the scientific name for the hemp plant. There are many different kinds of cannabis. The leaves and flowers of each kind produce varying mind-altering and medicinal effects when smoked or consumed. The most talked-about strains of the hemp plant are cannabis sativa and cannabis indica.

MARIJUANA is a Mexican slang word for cannabis leaves and flowers (aka buds).

HASH, short for hashish, is made of pressed resin from cannabis buds, and is therefore stronger in effect.

You may have heard.

You may have heard a variety of claims about cannabis in the media or in everyday conversation. For instance, you may have heard that cannabis use causes cancer or leads to quitting school. You may have also heard that the risk of developing cancer is low for cannabis smokers and that the drug can help relieve anxiety about school.

As a parent, making sense of these conflicting claims can be confusing. While there is at least some truth in almost all of them, accurate and balanced information about cannabis is more complex than simple statements.

There are no simple answers to explain the ways cannabis use may affect people’s minds, bodies, relationships and future opportunities. Why? Because people are complex beings, and our choices and behaviours are complex too.

Even if you have only limited experience with drugs, you likely know more than you think about the key issues. Most people, for example, understand intuitively that all drugs can be both good and bad. Even medication recommended by a doctor can cause harm, especially if not taken properly. When it comes to cannabis, almost everyone knows people who have had fun or benefitted in some other way from using cannabis or other drugs. Likewise, most people know of someone who has had bad experiences.

While most drugs are useful in some way, all drug use carries some risk. Generally, it is safest not to use any drug unless one can be sure the potential benefits clearly outweigh the potential harms. This includes assessing the context and reasons for use.

It can help to think of drug use as occurring within a matrix with two separate axes representing potential benefit and potential harm (see the illustration). Different types of use have different benefit/harm profiles, but even these change depending on many factors.

The potential that drug use might lead to certain harms and/or benefits is influenced by several things:

More drug equals more risk. Increased risk is linked with a greater amount and more frequent drug use, and higher strength of a drug.

Younger age equals more risk. The younger a person is when they start using a drug regularly, the more likely they are to experience harms or develop problematic substance use later in life.

Places, times and activities influence risk. Trying cannabis with friends at a weekend party and walking home later is less likely to result in harm than smoking cannabis on school property or driving under the influence.

The reasons young people use cannabis are important. Curiosity or experimentation often lead only to occasional use. Youth may use cannabis as a way to feel better, reducing anxiety in social situations and helping them connect with friends. While using cannabis can help reduce the symptoms of anxiety and depression, if young people use cannabis regularly to ease troubling feelings, use can become problematic. If a youth uses cannabis to perform better at school or fit in with a particular group, they may be listening to others, rather than valuing their own needs and wants, which can result in poor choices.

The reasons a young person uses cannabis, family history, the context, amount and way in which they use the drug all contribute to whether that use is beneficial, harmful, or both. Risks related to cannabis use vary from person to person, and sometimes, from day to day for a particular person. This can make deciding if, when and how to use cannabis difficult. Parents often have to weigh potential benefits and harms, and guide decisions in their particular family situation.

So, with this in mind, and in light of what the research tells us, let’s take a closer look at some of the common claims about cannabis.

PSYCHOACTIVE SUBSTANCES are drugs that affect our central nervous system (especially the brain) and make us see, think, feel, and behave differently than we usually do.

Common claims about cannabis

The human brain begins to develop in the womb but is not fully formed until well into adulthood. Drugs influence the way our brains develop. Regular cannabis use at an early age may have negative effects on brain development.

All psychoactive substances, from caffeine to heroin, have an immediate effect on the brain. The negative effects of cannabis, however, are much less than the effects of some substances such as alcohol.

While the negative effects of cannabis on the brain are often minimal and reversible, exposure to psychoactive substances during development should be minimized.

Available evidence cannot answer whether or not cannabis causes psychosis. But it does reveal an association between the two, with greater risk of psychosis for people who use cannabis frequently.

Cannabis may be one factor that interacts with other factors, such as a vulnerability to psychosis. For instance, someone with a family history of psychosis may be more sensitive to the potential psychosis-producing properties of cannabis than people without this vulnerability in their family.

That said, for some people, cannabis use can result in short-term psychotic symptoms such as unusual perceptions and feelings (e.g., they may hear voices or think someone is trying to harm them). Cannabis use can also negatively affect a person living with a psychotic disorder such as schizophrenia.

Studies on the effects of cannabis use on depression are also inconclusive. Some evidence suggests a link between frequent cannabis use and depression. But it is not clear how much of the relationship is based on cannabis use and how much is due to other factors such as family and social problems, living in poverty and other situations that may be beyond the person’s control.

Even though cannabis smoke contains carcinogens (cancer-causing toxins), the risk of developing some cancers (e.g., mouth, tongue and lung) is less for cannabis smokers than tobacco smokers. This is because cannabis smokers tend to smoke less. Cannabis smokers typically smoke one to three cannabis cigarettes a day compared to 10 to 30 tobacco cigarettes by tobacco smokers.

Another factor is related to the properties of the cannabis plant. For example, cannabis contains chemicals called cannabinoids, which some scientists think play a protective role against cancer in the lungs.

While there is an association between cannabis and quitting school, the linkages may be the result of common factors— personality traits or family issues, for example—that increase the risks of both cannabis use and dropping out of school. Or school policy related to cannabis use may be the cause. For instance, a zero-tolerance school policy for drug use, which isolates suspended students from their peers and teachers, may be more likely to lead to a student dropping out than drug use itself.

While there is an association between cannabis use and the use of other illicit drugs, the apparent linkages are related to personal, social and environmental factors rather than the effects of the drug.

Personal factors include particular personality traits (e.g., sensation seeking) which might drive a young person to use cannabis and go on to try other illicit drugs. Or a young person might try cannabis to relieve symptoms of a mental health problem (e.g., anxiety) and experiment with other substances to see if they have the same effect.

Social and environmental factors related to the use of other illicit drugs include how acceptable particular drugs are in the young person’s social group, and how available they are in their community.

As parents, thinking about cannabis and making decisions with your family can be a complex and challenging task. Personal history and attitudes to drug use, family values, medical history, legal status, community mores, and individual desires are factors that can affect what you choose to do. Thoughtful consideration of the issues can take some time. It is important to remember that you will make the best decision you can at that moment. You can re-evaluate your position and make different decisions as the situation and information available changes.

Is cannabis legal?

Cannabis is regulated in the province of BC. You must be 19 or over to purchase, possess or use cannabis or cannabis products for non-medical purposes in BC. It is illegal to sell or give cannabis to people under 19. People under 19 may not legally possess cannabis unless authorized to use it for medical purposes by their health care practitioner. Access to medical cannabis is regulated under the Access to Cannabis for Medical Purposes Regulations (ACMPR). Under the ACMPR, Canadians (including those under 19) who have been authorized by their health care practitioner to access cannabis for medical purposes are able to purchase safe, quality-controlled cannabis from one of the producers licensed by Health Canada, produce a limited amount of cannabis for their own medical purposes, or designate someone to produce it for them.

For more information on cannabis regulations in BC visit:

Data on the potency or strength of cannabis is limited, but the available evidence suggests there is a wide range in levels of THC (the main psychoactive ingredient). While there has been an increase in the average THC level over the past two decades, the rise has not been dramatic. Increases in THC levels are primarily related to selective breeding and more advanced cultivation techniques.

While the long-term negative effects of higher-potency cannabis on respiratory health or mental health are unknown, some researchers point out that using smaller amounts of higher potency cannabis reduces a person’s exposure to smoke and toxins and therefore might reduce risks. Clinical studies have shown that smokers regulate their dosage according to the strength of the cannabis by taking smaller or fewer puffs and/or inhaling more air with their puffs.

Cannabis purchased through government outlets in BC is tested for quality. If purchased from a dealer or friend the THC content may not be known, and people may use more than desired, and, in doing so, may experience negative consequences.

What is THC?

THC is short for the chemical compound delta-9-tetrahydrocannabidinol. THC is the most talked-about active ingredient in cannabis because it delivers the “high” feeling associated with using the drug.

Cannabis affects driving ability, including reaction time, lane maintenance, information processing, speed and distance estimation, eye movement control and attention. It also causes fatigue, which is itself a driving hazard. For these reasons, it is safest to avoid driving for three to four hours after using cannabis.

Cannabis in combination with even small doses of alcohol is a greater threat to safety than either drug used alone.

In the three to four hours after using cannabis, a person may have problems remembering or learning things. If a young person uses cannabis before or during school or work, these effects could impair their ability to do well in school or perform at work. However, most of the evidence suggests that any long-lasting effects on learning and memory are minimal.

Any kind of smoke can irritate the respiratory tract. People who smoke cannabis on a regular basis can develop inflammation in their respiratory tract (the part of the body involved in breathing). This can put them at risk of chronic coughing, shortness of breath and wheezing.

Using a device called a vaporizer can reduce the risk of respiratory problems. But “safest” does not mean “no risk.” Using a vaporizer only reduces smoking-related risks, not those related to the drug itself.

Comparing common ways to use cannabis

Some ways of smoking cannabis are safer than others. For example, using unfiltered joints is less risky than using water pipes (aka bongs) and joints with cigarette filters.

With unfiltered joints, cannabis smokers inhale less tar and more THC, the active ingredient in cannabis. Cigarette filters and water pipes reduce the THC, leading smokers to inhale more vigorously and increase the amount of tar in their lungs.

Vaporizers are the safest way to use cannabis. They release THC as a fine mist while reducing the toxic by-products of smoked cannabis. Ingesting cannabis also avoids the risks related to smoke and toxins but introduces other concerns. For instance, it is harder to find the right dose because it takes longer for the body to absorb the THC. This can result in a person using more than they intended and maybe having a negative or even scary experience.

While most people who use cannabis do not progress to problematic use, those who use cannabis frequently (daily or near daily) over a period of time may be putting themselves at risk of dependence.

A person may be dependent if they feel like they need to use cannabis just to feel normal and function during the day. People who stop using cannabis after regular use can experience mild feelings of withdrawal. Common symptoms of cannabis withdrawal are restlessness, nervousness, irritability, loss of appetite and difficulty sleeping.

The risk of developing dependence is higher for those who start to use cannabis regularly at an early age.

While some people worry that cannabis sold on the streets may be laced with crystal meth or other unpredictable substances, there is little evidence of this happening.

It is important to know the source of your cannabis. Buying from government distribution centres is safest.

Exploring medical cannabis use

Cannabis has been used as a medicine in many parts of the world for thousands of years. These days, many people in Canada want more evidence about what cannabis is (and is not) effective in treating, and the best way to deliver that treatment.

As it stands today, there is scientific evidence of the therapeutic benefits of cannabis for the following conditions: anti-spasm for multiple sclerosis, anti-convulsive for epilepsy, anti-nausea for chemotherapy, and appetite stimulant for people experiencing extreme weight loss. Recent research has shown cannabis is effective in managing pain.

Although cannabis can impact mental health in certain circumstances, some people with a mental health problem use it to relieve the symptoms of their condition or the unpleasant side effects of their medication.

When it comes to youth, research suggests that young people may be using cannabis for reasons that are similar to those of adults. Some studies suggest that youth experiencing mental health problems might be seeking relief through cannabis use. Mental health issues such as depression, insomnia and anxiety were reported as significant problems that interfered with their ability to function at school and with family and friends.

More research is needed to understand whether cannabis may have a place among treatment options for mental health problems such as anxiety and ADHD. For instance, evidence shows that cannabis has the potential to both increase and reduce anxiety. Some researchers believe these conflicting effects may be a reflection of the various cannabinoids in cannabis.

THC and other compounds in cannabis—notably CBD or cannabidiol—are being studied for their healing potential. Researchers believe that the ratio of THC to CBD is a crucial factor in how cannabis affects a person’s mind and body.

You and your child

When you’re thinking about talking with your child about drugs, knowing about some of the risks (and benefits) of cannabis use may help you feel more prepared. But it is not the most important way you can help your child navigate their world, a world where drug use is common.

More than information about cannabis, what your child needs is YOU. Research suggests that one of the most important factors in healthy child development is a strong, open relationship with a parent.

Intuitively, most of us already know this. But sometimes it helps to remind ourselves that it is our attention, love and patience that really count. It may also be helpful to remember that, ultimately, our goal as parents is to find ways to inspire our children to want to communicate with us—about cannabis or anything else.

Opening up a discussion about cannabis may be one way to strengthen your relationship with your child. It may encourage open lines of communication about other topics too. Inviting and allowing open, honest conversation about cannabis (or any other subject) makes your child know that what they are thinking, feeling and experiencing matters to you.

The exact words you use are less important than the underlying message you are sending—engaging in conversation with them says that you want to establish a connection with them, one that you hope lasts for a long time.

Connecting through conversation

Talking about cannabis or other drugs may not always be easy, fun or comfortable. But it may help to keep in mind that most people with kids struggle with parenting at least some of the time. No matter what you are going through as a parent, chances are there are others going through the exact same thing. In other words, you are not alone in your fears and frustrations—or in the joys and triumphs—of being a parent.

Starting a conversation

Some parents wonder when, where and how to start a conversation about cannabis. They ask themselves or others, “What age is the right age to start talking about drugs?” or “Should I ask the questions or should I wait until my child asks me something?”

Every child is different, so there is no “right age” to start talking about cannabis. But it makes sense to have your first conversation before your child is likely to try using cannabis. That way, you can establish a connection and share your expectations before they are exposed to any risks associated with cannabis.

There is no rule about how or where a conversation about cannabis should start either. But considering how often drugs are talked about on TV, in the newspaper, on social media, and at school, the subject might easily be brought up naturally while watching a movie together or while swapping stories about what happened at work and school that day.

Another “natural” way to start a conversation about cannabis is to bring it up in the context of other drug use. For instance, if you are planning to visit a relative who uses tobacco, you could inform your child about it and ask them what they know about smoking or how they feel about smoking. Or if you are having a beer or taking medication, you could ask, “Why do you think some people accept the use of alcohol and medication but not cannabis?”

It may be more comfortable to talk when you are not sitting across the table looking directly at each other. Try starting a conversation in the car or on the basketball court. You could say, “I’ve heard things on the news about kids smoking pot at school. How about your school? How does your principal deal with students who use drugs?”

Monitoring your motives

The goal of open communication is to get your child talking and sharing their thoughts and feelings with you. Ideally, they will one day ask you what you think and feel about things too. Establishing a connection through conversation is more important than assessing the details of what they tell you. After all, it is not really an open conversation if you are only inviting your child to talk so you can jump on them for ideas you do not like.

Practising good conversation skills

Your child, like anyone else you talk to, will be a better conversation partner if you stick to some basic rules about communication.

Be a good listener. Avoid the temptation to shower them with wisdom, and let them do at least half of the

Acknowledge their point of view. This does not mean you have to agree with what they say, but instead, to try not to react in a way that will shut down their desire to tell you how they think and feel about things.

Use open-ended questions that encourage reflection and the expression of feelings and views rather than simple yes/no answers.

Be clear about your expectation. Being honest about how you think or feel about cannabis use, and why you think or feel that way, can offer a broader perspective to your discussion.

??Keep them from tuning out. Avoid “lecture mode” and judgmental comments, and keep in mind that exaggerating the negative aspects of cannabis or any drug will not work for a child who has witnessed or experienced its positive effects.

“We know when we’ve screwed up. We don’t need to hear about it for hours. It’s embarrassing enough knowing we’ve done something we shouldn’t have and that our parents are mad about it.”

Responding to your child’s cannabis use

Discovering (or suspecting) your child has been using cannabis or any other drug can be scary, especially if you sense that it is not just part of “normal” experimentation.

While it can be tough to resist the urge to go wild with worry or anger, the best thing you can do for your child is to respond responsibly. It is important not to let your concerns harm the relationship and the trust you have with your child.

Stay calm

Yelling and making threats will not help the situation. If anything, “freaking out” will give your child another reason to hide things from you. Searching their room or personal belongings may harm the trust between you and your child.

Talk to your child

Sit down with them and tell them how you feel. If they are high, wait until the effects have worn off so you can have a more meaningful discussion. Say, “I’m worried because. ” or “I’m afraid because. ” Then give your child an opportunity to express their own feelings. Make sure they know you are really listening. And allow them time to think things through before speaking.

Learn why your child is using

Find out what led them to try cannabis in the first place. Was it because their friends were using it and they wanted to fit in? Was it for the “buzz” that comes from having an altered state of consciousness? Was it because they wanted a way to escape? Was it to manage symptoms of anxiety or other mental health problems? If so, you might want to consider seeking help from a mental health professional. It may also be helpful to find out how often your child uses cannabis.

Understand the difference between a youth who uses drugs and a youth with a drug problem

Young people use cannabis because they feel it benefits them. The most common reasons youth use cannabis are:

To feel good—Youth may use cannabis to feel more social, celebrate or relax. Using cannabis to feel good is associated with moderate use. There is still some risk, as there is in life in general.

To feel better—Cannabis can help reduce anxiety in social situations or when trying to connect with others or reduce symptoms of chronic anxiety or depression. If young people use cannabis regularly to deal with troubling feelings, then use may become problematic.

To do better—Some young people feel pressure to improve their performance, “get going” or “keep going.”

To explore—Young people particularly may use cannabis out of curiosity or to “walk on the edge,” trying something new and different.

It is important to keep in mind that sustained drug use problems are most common among people who feel isolated or marginalized. Youth without connections or meaningful relationships in their lives may seek solace in “feel-good” drugs. On the other hand, even well-connected young people can get into serious trouble from using too much or in the wrong place.

Offer alternatives

If your child is using drugs because they like the buzz, you may want to suggest activities that will naturally boost their adrenaline levels, such as rock climbing or mountain biking. If your child is using cannabis to calm themselves or to relieve feelings of anxiety, you could help them explore calming or meditative activities, such as yoga, running and swimming.

Lower the risks

A child who is using cannabis may need help learning to manage the risks and use the drug in the safest way possible. One way to help your child lower the risks related to using cannabis is to have a conversation about safer ways to smoke (see Quick tips for safer cannabis use). Another way is to discuss safer contexts and settings for use. Allowing your child to smoke cannabis at home may help to provide a safer environment but it is important to weigh the risks involved.

If your child is engaging in risky activities such as using cannabis at school or selling cannabis, it is important to talk with them about why they are engaging in these activities so that you can assess the level of risk, help them think through the consequences and identify alternatives. For example, if your child is selling cannabis to make money, talk with them about safer ways to earn an income.

“It didn’t make me want to use drugs. I liked that they were honest with me.”

Quick tips for safer cannabis use

Avoid smoking cannabis with tobacco

Avoid deep inhalation or breath-holding

Use a vaporizer

If smoking cannabis, use joints rather than water bongs

Use a small piece of rolled unbleached cardboard as a filter to prevent burns

Only use cannabis purchased from a trusted source

“I wouldn’t want my parents to tell me if they used drugs. I’d be embarrassed.”

Consider what to share (or not share) about your past

Many parents want to know if it is good or bad to tell their children about their own experiences with cannabis or other drugs. The answer is “it depends on your child and situation.”

One thing to think about is your motive for talking about your past. Are you telling them because you want to warn or frighten them in some way? Are you telling them because they asked and you do not want to lie to them? Are you telling them because you feel it might enhance your relationship in some way?

Another thing to consider is that some young people have a hard time seeing how any of their parents’ experiences are relevant to those of young people today. They may simply tune out when they hear stories about your past because they see no relationship between then and now.

Keep the art of motivation in mind

While no parent is 100% responsible for their child’s choices and behaviours, part of our job is to try to influence our kids in positive ways. One way involves checking in with them about their goals—over the next semester or year or even longer—and getting them to articulate how their use of cannabis or other drugs might impact those goals.

Taking a motivational approach is less about pressuring your child to change their cannabis use and more about supporting their internal reflection on their possible need and ability to change. It means steering a conversation toward possibility and action. And it is light in spirit and tone because it involves imagining success in the future.

In short, rather than make your child say and do what you want, help them identify what they want—to earn money, get a driver’s licence or graduate from high school—and support their efforts. You might need to help them understand what is involved in reaching a goal, and help them identify both internal and external resources they can draw on to ensure their success.

Give it time

It will likely take more than one conversation for you to understand your child’s drug use. But the good news is that, over time, you might discover your child has less of a problem than you thought. That is, your teen could very well be experimenting with cannabis the way many young people do without ever developing a risky or harmful pattern of use.

If a harmful pattern is emerging, you will need to be even more patient. But it may help to consider this: the path to your child’s drug use took time to build, so it makes sense not to expect a quick fix. A harmful pattern of drug use may be related to life challenges—feelings of failure or a lack of connection at school or with loved ones—that sometimes take a great deal of work to resolve. It might even be related to physical and mental health issues.

Signs of risky or harmful cannabis use

using regularly at an early age

daily or near daily use

using during school or work

using as a major form of recreation

using to cope with negative moods

experiencing chronic coughing, shortness of breath, wheezing or psychotic symptoms

NOTE: A young person may have one or more of these signs without having a short-term or long-term problem with cannabis. However, the more signs, the higher the risk.

Seek help

Not every parent is equipped to handle drug use issues on their own. If you need help understanding or communicating with your child, look for local resources and organizations that can assist you. You could try talking to

a school counsellor

your family doctor

your regional Health Authority

the Alcohol and Drug Information and Referral Service at 1-800-663- 1441 (BC) or 604-660-9382 (Greater Vancouver)

“The counsellor helped my child see he had other interests besides cannabis. And we learned to look at things in a more balanced way. We realized our child had more than just his pot-smoking friends in his life. He also had his sports friends and many other associations with people who didn’t use cannabis.”

In summary, try to remember.

As a parent, you are a powerful influence in your child’s life. Your approach to life, and how you deal with good things as well as difficulties, provides multiple opportunities for your children to learn how to be human, make mistakes (whether you want them to or not) and the process of making good decisions. Life presents us with many challenges each day. How to deal with drugs, including cannabis, may be one of those issues.

There are many things to consider, and you may struggle to make good decisions about complex issues like cannabis. Responsibilities to protect, support, and guide your children must be balanced with your values and the changing social and cultural realities of the twenty-first century. Reviewing your thoughts and feelings about cannabis, your personal history with it (did you use cannabis, do you still use it and why?) and the reasons your child is using cannabis are important considerations in thinking about what to do.

As noted earlier in this guide, young people use cannabis because they see benefit in doing so. They use cannabis to feel good, feel better, do better or explore. Entering into dialogue with your child about the benefits they receive from using cannabis will assist you to gather information and develop a mutual understanding that will help you make a good decision together about cannabis. In this process you may also discover your child has mental or physical health issues which may need to be addressed. Discussing your and your child’s concerns in the context of an open, caring and respectful relationship makes space for further dialogue on cannabis, and other issues that arise in the future.

For further information and supports please check out the resources listed on the following page.



The following resources are available on the Here to Help website:

Other websites to visit

Canadian Institute for Substance Use Research

Dedicated to research and knowledge related to substance use, mental health and well-being. The CISUR website provides fact sheets and self-help tools to help British Columbians make decisions about their well-being. The site also includes resources to support schools, campuses and communities to take effective action in addressing the impact of substance use.

Canadian Mental Health Association (BC Division)

Promotes the mental health of all British Columbians. The website provides self-help resources, personal stories and discussion of public issues related to mental illness, such as housing, employment and discrimination.


Provides a variety of supports for families and those who work with families. The website includes resources to promote greater understanding and increased collaboration among all involved in family well-being.

The Foundry

Foundry offers young people ages 12-24 health and wellness resources, services and supports – online and through integrated service centres in seven communities across BC.

Kelty Mental Health Resource Centre

Offers information and resources on mental health and substance use issues affecting children and youth including resources for parents and caregivers, healthcare professionals, school professionals, youth and young adults.

Cannabinoid exposure during pregnancy and its impact on immune function

Address for correspondence: Venkatesh L. Hegde, PhD, Department of Radiation Oncology, The Houston Methodist Research Institute (HMRI), 6550 Fannin St, Smith 08-077, Houston, TX 77030, Phone: 803-447-2351, Fax: 713-790-3755, [email protected]


Cannabinoids are the most commonly abused illicit drugs worldwide. While cannabis can be beneficial for certain heath conditions, abuse of potent synthetic cannabinoids has been on the rise. Exposure to cannabinoids is also prevalent in women of child-bearing age and pregnant women. These compounds can cross the placental barrier and directly affect the fetus. They mediate their effects primarily through G-protein coupled cannabinoid receptors, CB1 and CB2. In addition to significant neurological effects, cannabinoids can trigger robust immunomodulation by altering cytokine levels, causing apoptosis of lymphoid cells and inducing suppressor cells of the immune system. Profound effects of cannabinoids on the immune system as discussed in this review, suggest that maternal exposure during pregnancy could lead to dysregulation of innate and adaptive immune system of developing fetus and offspring potentially leading to weakening of immune defenses against infections and cancer later in life. Emerging evidence also indicates the underlying role of epigenetic mechanisms causing long-lasting impact following cannabinoid exposure in utero.

Keywords: Fetus, immune system, marijuana, metabolites, neurological, pregnancy, perinatal, prenatal, substance abuse


Cannabis and synthetic cannabinoids are considered one of the most common drugs of abuse [1–3]. There has also been an intense public interest with regard to their health benefits and a greater acceptance of medical cannabis in recent years [4, 5]. The current decriminalization and legalization efforts for the recreational use of cannabis as well as a renewed interest in its therapeutic use are expected to lead to an increase in the prevalence of exposure to these drugs in the coming years [6, 7]. These call for a clear understanding of risks of cannabinoid exposure during pregnancy. Historically, the constellation of effects of cannabinoid use during pregnancy has not received enough attention. While the early and long-term developmental and neurological adverse effects of prenatal cannabis abuse have been known for some time, the profound immunological implications are only beginning to emerge in recent literature. In this review, we discuss the prevalence and recent trends of abuse of cannabis and synthetic cannabinoids during pregnancy and address their impact on the endocannabinoid system (ECS) and immune function of the developing fetus and offspring. We will discuss the possible underlying mechanisms involving cytokines and cells of the immune system. Further, we will highlight the emerging role of epigenetic mechanisms of immune dysregulation caused by maternal exposure to cannabinoids during pregnancy.

Cannabis and synthetic cannabinoids

Cannabis (or marijuana) refers to the dried leaves, flowers, stems, and seeds from the plant Cannabis sativa, which contains the major psychoactive chemical delta-9-tetrahydrocannabinol (Δ 9 THC) as well as other related compounds collectively called phytocannabinoids ( Figure 1 ) [8–10]. It has been used for centuries not only for recreational purposes but also for its actual as well as perceived medicinal benefits [11]. It is believed to be beneficial in symptomatic relief of a variety of ailments. For instance, the use of cannabis and cannabis-derived cannabidiol (CBD) preparations for effective alleviation of seizers in children with epilepsy who do not respond to other medications is well known [12]. Cannabis and Δ 9 THC are also effective in providing relief from nausea, vomiting and loss of appetite in cancer patients undergoing chemotherapy as well as in AIDS patients [13]. In fact, the synthetic Δ9THC such as Dronabinol (Marinol™, Syndros™) and Nabilone (Cesamet™) are FDA approved drugs as antiemetics and orexigenics for this purpose. A mixture of Δ 9 THC and CBD (Sativex®) is approved for medical use in Europe and Canada for treating spasticity and neuropathic pain in multiple sclerosis (MS) patients [13]. Potent activity of cannabinoids in reducing inflammation has also been demonstrated in various preclinical models [14], and there is an interest in developing cannabimimetics as novel anti-inflammatory therapeutics.

Chemical structures of major cannabinoids. Phytocannabinoids are natural cannabinoids derived from Cannabis plant. Synthetic cannabinoids are potent cannabimimetics commonly present in designer street drugs such as K2 or Spice. Natural cannabinoids endogenously produced in humans and other animals are referred to as endocannabinoids. Most cannabinoids typically signal through cannabinoid receptors, CB1 and/or CB2.

Natural cannabis and a number of cannabinoid compounds including Δ 9 THC and CBD are classified as Schedule I substances based on the United States federal Controlled Substances Act. It is illegal to cultivate, possess, trade and consume cannabis in majority of the countries worldwide, although the extent of implementation of such laws, and hence the prevalence of its use may vary widely. Nevertheless, it is considered the most widely cultivated and trafficked drug of abuse. According to the World Health Organization, cannabis is consumed by ~147 million people or nearly 2.5% of the global population [15]. In the United States, cannabis is the third most widely abused drug by adults, next to alcohol and tobacco. However, recent surveys since 2010 have also found that adolescents smoked cannabis more than cigarettes [16]. Approximately 46% of young adults (ages of 18–34 years) have used cannabis in their lifetime; and 2–3% of the population consumes cannabis on a daily basis [17]. The prevalence of cannabis use has also been increasing among youth and teens since 2007 [16, 18, 18–20]. There have been increasing efforts in recent years towards easing restrictions on both medical and recreational use of cannabis. Several states in America have legalized it for recreational use, and 28 states have now passed laws allowing medical cannabis for certain health conditions [21]. With more states expected to join this trend, the cannabis use and abuse is anticipated to increase. Moreover, the amount of Δ 9 THC in cannabis has increased over the past decades, because of selective breeding practices for higher psychoactive content. Compared to approximately 4% in 1980s, Δ 9 THC concentrations in new cultivars of cannabis tremendously increased to about 15% in 2012 [22].

An alarming rise in the availability and abuse of highly potent synthetic cannabinoids has been considered as a public health emergency, with increasing number of overdoses and emergency room visits in large metropolitan areas [19, 23, 24]. Synthetic cannabinoids are mind-altering chemicals or mixtures of chemicals structurally related to Δ 9 THC that are sprayed on dried and shredded plant material, and sold. They are known by street names such as fake weed, K2 or Spice, often wrongly promoted as legal cannabis. Synthetic cannabinoid analogs such as JWH-018, JWH-073 or HU-210 ( Figure 1 ) are some of the most commonly found chemicals in these products [25, 26]. They are also sold as herbal or liquid incense to be vaporized and inhaled in e-cigarettes and other devices. Their abuse trend has also been associated with increasing popularity of e-cigarettes and vapes among teens and younger population [19]. Synthetic cannabinoids are much more powerful than cannabis or Δ 9 THC, sometimes over 100 times stronger with potent psychoactivity and likely, with a myriad of other known and unknown adverse health effects on human body [27–29]. For example, 11-hydroxy-Δ8-THC-dimethylheptyl (HU-210) is a remarkably potent synthetic agonist which has high affinity for both CB1 (Ki 0.0608 nM) and CB2 (Ki 0.524 nM) receptors [30]. It also exhibits high relative intrinsic activities at these receptors. Moreover, HU-210 is known to exhibit long half-life and prolonged duration of action in vivo. The high affinity and efficacy at cannabinoid receptors have been mainly attributed to the replacement of the pentyl side chain of Δ8-THC with a dimethylheptyl group in HU-210 [30, 31].

Cannabinoid abuse during pregnancy

Cannabis is the most widely used illicit drug among women of childbearing age. In recent years, cannabis use appeared to increase among women in their reproductive years. In one of the Monitoring the Future Studies by NIDA, 10.4% of women aged 19 to 32 years reported using cannabis [32]. A recent survey has documented that approximately 4.9% of women of childbearing age regularly smoke cannabis [33]. The prevalence of substance abuse during pregnancy may vary from 5–16% [34]. It is estimated that five million women of childbearing age use illicit drugs and that approximately half a million infants in the United States are exposed to one or more illicit drugs in utero. Hence, the impact of maternal substance abuse on both the mother and offspring is of major public health concern. Based on National Pregnancy and Health Survey conducted by National Institute on Drug Abuse (NIDA), the prevalence and substance use patterns among women delivering live-born infants in the US, the self-reported cannabis use during pregnancy was 2.9% compared with 0.9–1.1% for cocaine [35, 36]. While the proportion of substance abuse treatment admissions for pregnant women in the United States remained stable at 4% during 1992–2012, those pregnant women reporting cannabis use increased significantly from 29% to 43% [37]. These studies have also found that pregnant women who use illicit drugs are more likely to use cannabis compared to other substances. This is often due to the perception that cannabis may be less harmful to the developing embryo and fetus compared to other drugs such as cocaine, heroin, or methamphetamine. With the legalization and decriminalization of medical and recreational cannabis in several states, its use among women and during pregnancy is expected to further increase in the coming years [38].

Accumulating evidence suggests that cannabis exposure during pregnancy may significantly impact fetal brain development causing neurological impairments, hyperactivity, poor cognitive function and changes in dopaminergic receptors in children [35, 39–44]. Notably, recent experimental evidence in rodents point to significant impact of stimulation of cannabinoid system on learning and reward-related explicit memory [45, 46]. While cannabis use during pregnancy did not increase risk of perinatal mortality, regular use of cannabis throughout pregnancy was associated with significant decrease in birth weight [35, 47]. However, a recent study found that cannabis use, after adjusting for tobacco and other illicit drug use, was associated with neonatal morbidity or death [48].

Endocannabinoid system (ECS) and pregnancy

The effects of cannabis on reproductive and immune functions may be closely related to the processes that are modulated by the ECS. Endogenous cannabinoids (endocannabinoids) together with cannabinoid receptors, metabolic enzymes and membrane transporters form the ECS [49, 50]. Anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are the two major endocannabinoids ( Figure 1 ) [51, 52]. AEA is metabolized by fatty acid amide hydrolase (FAAH) to arachidonic acid (AA) and ethanolamine, while 2-AG is mainly degraded by monoacyl glycerol lipase (MAGL) to AA and glycerol [53, 54]. Although the precise mechanisms are not fully known, it is agreed that ECS plays a pivotal role in reproduction [55, 56]. The components of ECS are involved in fertilization, oviduct transport, implantation, embryo development, maintenance and immune regulation during pregnancy [57–59].

FAAH activity has been linked to early pregnancy success with a strong correlation between its decrease in maternal peripheral blood mononuclear cells and spontaneous miscarriage in women [60]. The levels and activity of FAAH were significantly lower in patients undergoing embryo transfer following in vitro fertilization who failed to achieve successful implantation as compared to those who became pregnant [61]. FAAH is considered as a critical metabolic gatekeeper of AEA levels in the uterus throughout menstrual cycle, as well as during pregnancy [62, 63]. In a major study, uterine AEA levels were shown to be highest during non-receptive stage and in inter-implantation sites, but lowest at the site of embryo implantation [64]. Thus, downregulation of AEA is associated with uterine receptivity, and its elevated levels with uterine refractoriness to embryo implantation. This suggests that the down-modulation of uterine AEA at the implantation sites may be the mechanism by which embryos protect themselves from detrimental effects of this endocannabinoid [64]. AEA also modulates decidualization of rat and human endometrial stromal cells [65, 66]. AEA signaling has also been shown to regulate sperm functions required for fertilization in human reproductive tracts [67]. Deregulation of metabolic enzymes of endocannabinoids following exposure to cannabis has been therefore implicated in potential negative impacts on human fertility [65]. In fact, Δ 9 THC is known to significantly influence bioactive lipid profile or induce endocannabinoid levels [68, 69]. Unlike endocannabinoids, Δ 9 THC is metabolized slowly and may mimic situations in which an excess of endocannabinoids are produced or when re-uptake or removal of endocannabinoids is impaired [58]. Further, THC and CBD can have non-CB1/CB2 targets which may produce a more complex signaling cascade and additional implications for pregnancy.

Several studies have explored the role of intricate endocannabinoids-sex hormone-cytokine regulatory axis during pregnancy [57, 70]. Sex steroid hormones, progesterone and estrogen, are involved in the maintenance of endocannabinoid levels [71]. Progesterone promotes lymphocyte FAAH activity involving transcription factors Stat3 and Ikaros, which results in lower AEA levels [72–74]. These studies indicate regulation of immune cytokine network by endocannabinoids during reproduction which appears to be one of the important mechanisms controlling implantation and the maintenance of healthy pregnancy [75]. Animal studies have shown the presence of constituents of ECS in early embryo before neurogenesis indicating its involvement in early embryogenesis [76–78]. Thus, maternal abuse of cannabis and synthetic cannabinoids can cause adverse reproductive, developmental and immune consequences also by significantly altering the components of the ECS.

Pregnancy and immunity

The maternal immune system actively tolerates the semiallogeneic fetus during pregnancy. This includes changes in local immune responses in the uterine mucosa as well as alterations in peripheral immune responses [79, 80]. The innate immune system is activated during pregnancy [81, 82]. Cells of the granulomonocytic lineage significantly increase during normal pregnancy and undergo phenotypic and functional activation [83], whereas the dendritic cell numbers decrease [84]. Further, the number of natural killer (NK) T cells and the production of interferon (IFN)-γ by NK cells is decreased in pregnant women [85]. Pregnant women are more sensitive to certain infections and immune dysregulation caused by either proinflammatory or immunosuppressive stimuli. Thus, a significantly altered immune system is essential during pregnancy for normal placentation and maintenance of a healthy pregnancy. However, interfering with the maternal immune system could disturb the balance between tolerance and immunity during pregnancy and may affect the outcome.

Prenatal cannabinoid exposure and immune dysregulation

Exogenous cannabinoids, such as Δ 9 THC, have been shown to cross the fetal-placental barrier in humans and other mammals [86–89]. Significant effects of prenatal, intrauterine exposure to cannabinoids on the growth and development of the fetus, as well as on learning and memory, neuronal, behavioral and endocrine aspects of the progeny have been studied and reviewed [43, 90–92]. In addition to its effects on central nervous system (CNS), cannabinoids also profoundly alter immune function [93–96]. While CB1 receptor is expressed in brain and CB2 in the peripheral tissues, immune cells express both the receptors [97–99]. Moreover, reproductive tissues such as the uterine endometrium, human placenta and ovaries express functional cannabinoid receptors [100–103]. However, only a few studies have investigated its impact on maternal and developing immune systems under normal or disease conditions. These studies as discussed below suggest that maternal Δ 9 THC exposure may have long-lasting effects on the immune system of the offspring.

T cells play a significant role in implantation, with the shift from Th1 to Th2 helper T cell response at the fetal-maternal interface contributing significantly to a successful pregnancy [104]. It is suggested that a Th2 shift inhibits Th1 cytokine responses, allowing the survival of the fetal allograft [105]. It has also been found that FAAH expression is regulated by the Th1 and Th2 cytokines, with IL-4 and IL-10 enhancing its activity and IL-2 and INF-γ reducing its expression [74]. A recent study has shown that expression of CB1 and CB2 receptors in B lymphocytes is differentially regulated during pregnancy [106]. Moreover, B cells from pregnant mice were shown to produce elevated levels of anti-inflammatory cytokine IL-10 following activation of CB1 receptors by select agonists [106]. Maternal exposure to synthetic cannabinoid HU-210 in rats was found to result in detectable changes in the development of the immune system, and long-lasting alterations to the functional status of the hypothalamus-pituitary-adrenal axis. Particularly, prenatal exposure to HU-210 caused reduction in the T-helper subpopulation in the spleen and a dose-related decrease in the ratio of T helper/ cytotoxic T cells in the peripheral blood of adult male offspring [107].

Murine fetal thymocytes express high levels of the CB1 and CB2 receptors [108]. Acute exposure to Δ 9 THC on gestation day 16 was shown to significantly impact fetal immune components as demonstrated by significant thymic atrophy and marked alterations in T cell subpopulations in fetuses on gestational days 16–18 as well as in pups on post-gestational day 1 [108]. Thymic atrophy was characterized by significant dose-dependent (20–50 mg/kg of Δ 9 THC) decrease in thymic cellularity which correlated with caspase-dependent apoptosis of thymocytes. Δ 9 THC exposure significantly decreased the number of single-positive CD8, double-positive CD4CD8 and double-negative T cell subsets of fetal thymocytes. Δ 9 THC (5–20μM) also induced apoptosis in ex vivo fetal thymic organ cultures in a dose-dependent manner. These effects were mainly mediated by activation of CB1 and CB2 receptors as in vivo receptor blocking experiments using intraperitoneal injections of CB1 antagonist SR141716A (20 mg/kg) or CB2 antagonist AM630 (40 mg/kg) one hour prior to Δ 9 THC (50 mg/kg) administration attenuated these immunological changes. Importantly, exposure to Δ 9 THC in pregnant mice had a significant and persistent effect on the postnatal immune response. For example, subchronic perinatal exposure to Δ 9 THC with the dosing regimen of 25 mg/kg on gestation day 16 and 10 mg/kg every day thereafter until the pups were born for a total of four injections resulted in significant decrease in thymic and splenic cellularity in 1-week-old offspring, thus negatively affecting the immune system of the progeny. Moreover, decreased proliferative and antibody responses to HIV gp120 antigens by peripheral T cells from the offspring demonstrated significant immune dysregulation. Thus, exposure to 20–50 mg/kg Δ 9 THC in pregnant mice seems to trigger profound T cell dysfunction in the developing fetus and the immune system of the offspring, thereby suggesting that cannabinoid exposure during pregnancy may cause significant and long-lasting effects on immune function [108].

Human epidemiological observations linking cannabis use, HIV immunity and development of AIDS have been contradictory. In a retrospective study that evaluated the link between cannabis use and sexually transmitted diseases in pregnant women entering prenatal care in which 86 women using only cannabis as an illicit substance were compared to 441 drug-free women with regards to the prevalence of gonorrhea, chlamydia, syphilis, human immunodeficiency virus (HIV), hepatitis B surface antigen, human papilloma virus, and herpes virus. No significant differences were found in the prevalence of these sexually transmitted infectious diseases between pregnant women who used cannabis and the drug-free pregnant women [109]. However, an association between cannabis use and HIV progression and the development of symptomatic AIDS was reported in homosexual men [110]. HIV positive men who progressed to AIDS and to have used cannabis for 3 months or more were more likely to have a lower percentage of CD4 T cells and a higher percentage of CD8 T cells [110]. However, several other studies reported no statistically significant links between cannabis or synthetic cannabinoids and HIV infection or associated immune parameters [111, 112]. For example, a randomized and placebo-controlled intervention trial involving 67 patients with HIV-1 infection, cannabis smoking and oral Dronabinol did not appear to adversely affect HIV RNA levels, CD4+ or CD8+ cell counts, or protease inhibitor levels [113]. In vitro studies on the effects of cannabinoids on HIV have also been contradictory. One study noted that several cannabinoid receptor agonists, including Δ 9 THC, may enhance HIV infection of a human T cell line [114], whereas others have reported that the synthetic cannabinoid receptor agonist WIN55,212–2 inhibited HIV expression in CD4 T lymphocytes and microglial cell cultures [115, 116]. However, in a hybrid mouse model in which human peripheral blood leukocytes were implanted into severe combined immunodeficient mice (huPBL-SCID), exposure to Δ 9 THC could suppress immune function, increase HIV co-receptor expression, and act as a cofactor to significantly enhance HIV replication [117]. HIV+ patients who were also cannabis users had lower circulating CD16 monocytes and IFN-γ-inducible protein 10 (IP-10) levels when compared to those not using cannabis [118]. Daily cannabis use was strongly associated with moderate to severe fibrosis in hepatitis C virus-infected individuals [119] and with liver fibrosis progression in patients with chronic hepatitis C [120]. The CB1 receptors were found to promote the progression of fibrosis as CB1 antagonism was able to attenuate liver fibrogenesis primarily by decreasing hepatic TGF-β [121]. CB1 and CB2 receptors have also been shown to play opposite roles in the pathogenesis of alcoholic liver disease via regulation of reinforcing properties of alcohol in the brain as well as hepatic cell injury and inflammation by endocannabinoids [122].

Immunomodulatory activity of both plant-derived and endocannabinoids have been also studied in animal models of inflammation such as allergic contact dermatitis, autoimmune hepatitis and graft-versus-host disease [14, 123–130]. Cannabinoids have been shown to typically act by suppressing proinflammatory cytokines, decreasing effector CD4/CD8 T cell population by inducing apoptosis and inhibiting their proliferation [124, 128]. Moreover, they can also upregulate certain chemokines or growth factors (G-CSF) and induce regulatory T cells or immunosuppressive myeloid cells [124, 127]. While most cannabinoids exert these effects via activation of cannabinoid receptors (CB1/CB2) [123, 124, 128, 130], CBD has been shown to function through vanilloid (Trpv1) receptors to ameliorate inflammation [127]. The robust anti-inflammatory activity of cannabinoids can have significant impacts during pregnancy. For example, use of non-steroidal anti-inflammatory drugs (NSAIDS) during pregnancy has been linked to miscarriages and other adverse outcome [131, 132]. According to a nested case-controlled study of 47,050 women, the risk of miscarriage was 2.4 times greater for those who took NSAIDS in early pregnancy [133]. The synthesis of prostaglandin is important in later stages of pregnancy and for fetal maturation [134]. Therefore, exposure to NSAIDS during the third trimester can affect fetal development and cause fetal ductal constriction [135]. Clinical evidence supports the association of changes in fetal ductus arteriosus flow and maternal consumption of foods rich in natural anti-inflammatory substances such as polyphenols [136–138]. Maternal dietary intervention during the third trimester of pregnancy by restricting potent anti-inflammatory foods for a period two weeks or more had a beneficial outcome with improved fetal ductal flow dynamics and reduced dimensions of the right ventricle [137]. Pro and anti-inflammatory conditions are tightly controlled in utero during pregnancy. Such fine-tuned regulation of inflammatory milieu is critical for optimal maintenance of pregnancy, fetal health, development and normal labor. While intrinsic changes in endocannabinoid levels appear to be an important component of this regulatory process, exposure to exogenous immunomodulatory cannabinoids could significantly alter this balance.

Increased frequency of mutant lymphocytes were observed in cannabis-smoking mothers and their newborns, suggesting a link between maternal cannabis smoking and somatic mutations, with a potentially elevated risk of developing malignancies [139]. Feinshtein et al., examined the influence of short-term exposure of human placental epithelial cell lines to CBD, and found that CBD inhibited placental breast cancer resistance protein function. Further, CBD significantly enhanced glyburide transport across human placenta ex vivo, suggesting that cannabinoids could enhance placental barrier permeability to other xenobiotics and endanger the developing fetus [140]. The association between maternal cannabis use and incidence of certain childhood malignancies such as rhabdomyosarcoma, astrocytoma and leukemia have been studied [141–144]. Trans-generational assessment of the effect of maternal cannabis use in 204 case-controlled women during and one year preceding pregnancy showed as much as an 11-fold increased risk of childhood acute non-lymphoblastic leukemia in offspring [141]. In cases of childhood acute myeloid leukemia, the risk of association was not observed with maternal cannabis use 3 months prior to or during pregnancy [89]. An evaluation of the self-reported use of recreational drugs in the mothers of 538 children with neuroblastoma showed that cannabis use during the first trimester of pregnancy was associated with significantly increased risk of neuroblastoma in the offspring, whereas its use during late pregnancy did not increase the risk. The association of gestational cannabis exposure with cancer incidence was particularly strong in children diagnosed with neuroblastoma before the age of 1 year [145]. However, these epidemiological studies have major limitations in that the data were mainly obtained by hospital surveys and information on amount of exposure was not available or dose-response evaluations were not performed, and therefore did not establish a causative link.

Potential impact of metabolites of exogenous cannabinoids

The detection of metabolites of Δ 9 THC and CBD in human hair and body fluids, and their precise quantitation methods have been well-developed particularly in the context of clinical toxicology and forensics of cannabis abuse [146–148]. However, unlike in the case of parent cannabinoids, there is limited literature on the biological activities of their metabolites.

11-Nor-9-carboxy-Δ9-tetrahydrocannabinol also known as THC-11-oic acid (11-COOHTHC) is the most abundant metabolite of Δ 9 THC [149–151]. As such 11-COOH-THC in body fluids is the clinical and forensic marker for cannabis exposure. Δ 9 THC is primarily metabolized by liver cytochrome P-450 (CYP450) isoenzymes into Phase I metabolites, which are oxidative and/or hydroxylated derivatives [152]. The initial oxidative metabolite is 11-hydroxy-Δ 9 THC (11-OH-THC), which is psychoactive. Further oxidative metabolism gives rise to 11-COOHTHC, which is inactive at CB1 and hence non-psychoactive [153]. This and other oxidized metabolites can also get converted to glucuronide esters as Phase II metabolites before excretion. 11-COOH-THC could be detected in the newborn meconium to determine the maternal exposure to cannabis [154], which suggested its placental transfer. Although 11-COOH-THC is psychotropically inactive, it exhibits analgesic and anti-inflammatory properties and hence considered as a biologically active metabolite. Similar to Δ 9 THC and CBD, 11-COOH-THC suppressed melatonin biosynthesis in rat pineal gland preparations ex vivo [155]. Orally administered 11-COOH-THC showed higher activity than Δ 9 THC in preventing platelet-mediated edema [156]. Moreover, 11-THC-COOH showed topical anti-inflammatory effects in vivo in experimental ear edema model in mice [157]. Certain synthetic cannabinoids such as ajulemic acid (AjA), endocannabinoids, and 11-THC-COOH have been shown to also influence eicosanoid biosynthesis. Endocannabinoids 2-AG and AEA can serve as a source of AA as well as metabolized by most eicosanoid biosynthetic enzymes, yielding additional lipids that regulate inflammatory cell functions [158]. AjA can increase the steady state levels of COX2 mRNA and AA release, and can selectively and markedly upregulate 15d-PGJ2, an eicosanoid which facilitates resolution of inflammation [159]. While AjA could induce 2–7 fold increase in the production of anti-inflammatory eicosanoid lipoxin A4 [160], 11-COOH-THC was found to inhibit cyclooxygenase and 5-lipoxygenase activities involved in prostaglandin biosynthesis, and hence decrease the production of proinflammatory prostaglandin eicosanoids [161].

Unlike THC, the metabolism of CBD is extremely complex, with more than 100 different metabolites identified [162]. The major metabolites of CBD are water soluble, hydroxylated 7-COOH derivatives [163]. Similar to natural enantiomer (−) CBD, the 7-COOH metabolites had very low affinities for CB1 and CB2 receptors. Whereas, those derived from synthetic (+) CBD enantiomer exhibited high (Ki = 13.2 nM) and modest (Ki = 156 nM) affinities respectively for CB1 and CB2. Moreover, while both CBD enantiomers were good agonists of vanilloid (Trpv1) receptors, the 7-COOH metabolites showed no Trpv1 binding [164]. The 7-COOH CBD metabolites may also have anti-nociceptive and anti-inflammatory activities as they were found to inhibit the generation of nitric oxide and reactive oxygen species as well as production of TNF-α in vitro in a dose-dependent manner [164].

A number of human metabolites of synthetic cannabinoids have been reported [165, 166]. However, studies on their biological effects are limited. Mass spectrometric analysis of human urine specimens of individuals exposed to JWH-018 has identified monohydroxylated and carboxylated derivatives as the major metabolites, with hydroxylated primary metabolites exhibiting potent CB1 receptor agonistic activity [165, 167]. The metabolites of synthetic cannabinoids can also produce stronger activation of CB1 and CB2 receptors than Δ 9 THC, and may possess distinct pharmacology and higher toxicity [168–170].

While studies investigating the direct impact of metabolites of exogenous cannabinoids are lacking, their known biological activities as discussed above have the potential to interfere during pregnancy. It is likely that the immunosuppressive activity of bioactive cannabinoid metabolites may interfere with normal inflammatory changes and eicosanoid-prostaglandin homeostasis during pregnancy. Whether or not these metabolites affect fetal development or have specific neuronal and immune-related effects impacting the offspring needs further investigation.

Emerging role of epigenetic mechanisms

Epigenetics refers to stable, long-term alterations in the cell or individual that involves mechanisms of gene regulation by post-transcriptional and post-translational modifications, but not direct changes to the DNA sequence [171, 172]. The epigenetic regulatory machinery includes DNA methylation, histone modifications and non-coding RNAs. Recent studies have explored the impact of phytocannabinoids, synthetic cannabinoids and endocannabinoids on the epigenetic components [173–177].

Using a combined computational and experimental approach, it was shown that myocardial CB1 receptors were regulated by microRNA(miR)-494 and that CB2 receptors were targeted by miR-665, with miR-494 enhanced and miR-665 significantly repressed in chronic heart failure [178]. In Simian immunodeficiency virus-infected macaques, miRNA expression was profiled in intestines at 14, 30, and 60 days post-infection with or without chronic Δ 9 THC administration [179]. Chronic Δ 9 THC exposure was found to significantly increase the total number of differentially expressed miRNAs, selectively enhancing the expression of miR-10a, miR-24, miR-99b, miR-145, miR-149 and miR-187, that were found to target pro-inflammatory pathways, suggesting that the selective upregulation of anti-inflammatory miRNAs may contribute to Δ 9 THC-induced attenuation of gastrointestinal inflammation and maintenance of intestinal homeostasis [179].

The immunomodulatory effect of Δ 9 THC in experimental superantigen-elicited immune response in mice was shown to be mediated by epigenetic regulation [176]. In this study, changes in histone modifications in activated lymphocytes from mice following staphylococcal enterotoxin B superantigen challenge with or without Δ 9 THC administration were studied using ChIP-Seq approach. Global histone methylation and acetylation were found to be altered by Δ 9 THC, which caused increase in active histone modification marks (H3K4me3) in Th2-associated genes and of suppressive modification signals (H3K27me3) in Th1-associated genes, suggesting for the first time that Δ 9 THC might modulate immune response through epigenetic histone modifications. In humans, the regulation of increased proenkephalin (Penk) expression, which is an opioid neuropeptide gene, was found to be mediated via decreased histone H3K9 methylation in the brain nucleus accumbens of adults following adolescent Δ 9 THC exposure, thereby disrupting the normal developmental pattern of this epigenetic mark. It was suggested that epigenetic dysregulation of Penk underlies the long-term effects of Δ 9 THC particularly in the neurobiological mechanisms of vulnerability to abuse of other drugs associated with cannabis abuse [180]. Rotter et al., have investigated the CB1/CB2 receptor promoter methylation status in peripheral blood cells of individuals with Δ 9 THC dependence and non-smoking control subjects. A significant negative correlation between mean promoter methylation frequency and CB1 expression was noted with a higher CB1 expression associated with cannabis consumption. Thus, altered CB1 expression associated with Δ 9 THC dependence was found to be mediated by changes to promoter methylation status [181].

Our seminal study demonstrated that cannabinoid receptor activation by Δ 9 THC in mice leads to a rapid and massive expansion of CD11b + Gr-1 + myeloid-derived suppressor cells (MDSC) expressing functional arginase and exhibiting potent immunosuppressive properties both ex vivo and upon adoptive transfer in vivo [182]. Further, the induction of MDSCs by Δ 9 THC in vivo was associated with robust upregulation of chemokines, particularly G-csf and Cxcl1. Thus, induction of certain chemokines and MDSCs was identified as a major mechanism of immunomodulation by Δ 9 THC. MDSCs are the major immunosuppressive innate cell population induced in cancer, where they play a critical role in cancer immune escape [183, 184]. Epigenetic changes involving microRNA in MDSCs that are induced in vivo following exposure to Δ 9 THC have been studied in mice [175]. Δ 9 THC-induced MDSCs were found to exhibit distinct global microRNA expression profile compared to other myeloid cells and control bone marrow myeloid progenitor cells, with the targets of differentially expressed miRNA significantly associated with hematopoiesis and myeloid cell function Gene Ontology clusters as well as myeloid differentiation biological pathways. In fact, several of the altered miRNA were found to directly target crucial transcription factors involved in myeloid differentiation and function. Importantly, miRNA-690, highly overexpressed in Δ 9 THC-MDSCs, was found to target and regulate CCAAT/enhancer-binding protein α (C/EBPα), a master regulator of myeloid differentiation. The functional nature of this regulatory circuit was further confirmed by ex vivo miR-690 knockdown in primary MDSCs [175]. Moreover, endocannabinoid 2-AG has been recently shown to increase the presence and suppressive potency of MDSCs in brain [185], and AEA was shown to suppress Th17 cell-mediated experimental delayed type hypersensitivity response in vivo in mice by inducing IL-10 which in turn triggered a set of miRNA specifically targeting pro-inflammatory pathways [186].

Concluding remarks and Perspective

Currently accepted theories of the fetal origins of adult diseases involve in utero exposure and response to environmental factors that ultimately lead to persistent effects with increased susceptibility to certain diseases later in life. Although precise mechanisms are not completely known, accumulating evidence in recent years suggests the involvement of epigenetic regulatory pathways [187, 188]. Studies on the effects of cannabinoids on the epigenome thus far have been mostly performed in adults. As epigenetic changes are stable and have sustained effects, these early results suggest that cannabis abuse could have a trans-generational impact, and that such events early in life in utero might have a significant impact on fetal health and progeny, including the critical immune components ( Figure 2 ). Importantly, immune system and inflammation also plays a critical role in the etiology of number of neurological and psychiatric illnesses. Women during pregnancy could potentially get exposed to high potency cannabis and synthetic cannabinoids. Robust controlled human studies involving drug abuse patients on the specific effects of cannabis and synthetic cannabinoids on immune function in neonates and offspring are lacking. Future studies with a balanced approach are needed to examine the dose and duration-dependent effects cannabis components and synthetic cannabinoids on immune function and other health aspects to further clearly understand their harmful impact and pregnancy risks, as well as any potential beneficial effects.