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Effects of Cannabis on the Male and Female Reproductive System, and Fertility

Use of cannabis may affect human fertility, depending on gender, general health, socioeconomic status and several other factors. Here, we look at existing research on cannabis and human fertility, in order to provide readers with an accurate, up-to-date summary of the current state of scientific knowledge.

To understand how cannabis may affect fertility, we must understand the effect it has specifically on males and on females. We’ll start by looking at the effects on the male reproductive system, and then focus on the more complicated effects on female fertility.

Cannabis use and male fertility

Some studies on the effect of cannabis use on male fertility have indicated that regular use may reduce spermatogenesis (the production of sperm in the testes) and testosterone levels.

In 2012, the American Society of Andrology published a review of research on the effects of illicit drug use on male fertility. The researchers found that in the majority of studies, it was consistently concluded that cannabis use had a negative impact on male reproductive physiology.

Another study in 1992 (Vescovi et al.) found that levels of luteinizing hormone(LH), an important pituitary gland hormone involved in reproductive function, were reduced in male chronic cannabis users compared to a non-cannabis-using, age-matched control group. A previous 1986 study (Cone et al.) also found a significant reduction in LH levels immediately after smoking cannabis.

And an even earlier study (Kolodny et al, 1974) into testosterone levels in “chronic” cannabis users found that 6 of 17 subjects had oligospermia (low sperm count), and that average testosterone levels in the cannabis-using group were just over half that of the control group. The effect of cannabis on testosterone levels was observed to be dose-dependent.

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The endocannabinoid system and male fertility

Clearly, the endocannabinoid system has a role to play in the regulation of processes critical to male reproductive health, such as sperm count, testosterone levels, and levels of other key hormones such as LH.

For healthy adult males, it seems that use of THC does indeed cause some negative effects on fertility, which tend to increase with higher doses. However, THC’s endogenous analogue anandamide appears to be critical to the functioning of the male reproductive system.

The 2002 study found that sperm cells would bind to the agonist CP-55,940, demonstrating the presence of CB1-receptors. The study also concluded that the presence of THC and a synthetic anandamide analogue, AM-356, both reduced sperm motility in vitro. Interestingly, it was found that AM-356 exerted a biphasic dose-dependent effect on sperm motility, causing inhibition at high doses but hyperactivity at low doses.

Anandamide and the “capacitation” of human sperm cells

In a 1994 study, it was found that mammalian sperm, including that of humans, is actually incapable of fertilizing oocytes (eggs) immediately after leaving the testes. It requires a period of exposure to certain crucial hormones, enzymes and proteins on its journey through the vas deferens and ejaculatory ducts of the male reproductive system (as well as the reproductive fluids of the female vagina and oviducts) before becoming “capacitated” and able to fertilize an egg.

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The 2002 study provides strong evidence that the presence of the anandamide in the seminal fluid, and its ability to bind to the CB1-receptors of the spermatozoa, are key to the “capacitation” of sperm cells on their way to the ejaculatory ducts. It has to be present in the appropriate concentrations, though. If the level of anandamide is too high, it can instead have a dramatic inhibitory effect on the sperm cells’ ability to fertilize oocytes.

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Why is anandamide beneficial, while THC may not be?

Although THC and anandamide are both agonists of the CB1-receptors, they greatly differ in structure and therefore have different effects on certain metabolic processes. Anandamide has a much shorter half-life than THC (just a few minutes for anandamide compared to as long as 24 hours for THC). So while anandamide will degrade shortly after it contacts a receptor, THC can remain in nearby adipose tissue for much longer periods, and can continue to stimulate the receptors, ultimately causing overstimulation and potential negative effects.

As is so often the case with cannabinoid science, dosage is everything—and it may prove to be the case that very small doses of THC could benefit males who have reproductive issues that can be tied to low levels of anandamide.

Cannabis use and female fertility

While the effect of cannabis use on male fertility appears to be quite straightforward—with male chronic cannabis users being likely to experience some degree of impairment to reproductive physiology—the effect on the human female reproductive system is less clear-cut.

Female reproductive health is vastly complex in itself, as it not only comprises the ability to become pregnant but also the ability to carry healthy offspring to term and successfully give birth.

Past research has indicated that cannabis use may disrupt the menstrual cycle, suppress oogenesis (production of eggs in the ovaries) and impair embryo implantation and development. Chronic use of cannabis has also been repeatedly associated with lower birth weight (as much as a 50% increased risk), decreased birth weight and early (spontaneous) termination of pregnancy.

However, most of these findings are far from conclusive. Either the study included very few participants or confounding factors such as tobacco use aren’t taken into consideration. In fact, more recent research, like this review on infants who were exposed to marijuana in-utero, concludes there aren’t any adverse risks.

For example, a 1985 paper on foetal abnormality (Qazi et al.) after prenatal exposure to cannabis discussed five infants whose mothers acknowledged use of cannabis prior to and during pregnancy and who were born with various symptoms of growth retardation, neurological dysfunction and deformity. While it may provide helpful insight, such a small sample size is far from being enough to draw concrete conclusions, and correlation does not imply causation.

Other studies seen as providing evidence that cannabis use can cause foetal abnormalities are animal studies (Geber & Schramm 1969, Phillipset al, 1971) in which rabbits, hamsters, rats and mice were injected with vast doses of crude cannabis extract (as much as 666mg/kg in one instance!). Such massive doses of cannabis would be practically impossible for a human to consume through conventional means, and are essentially useless as a point of comparison.

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In fact, many early studies that indicated a correlation between use of cannabis (or other controlled substances such as cocaine) have been later contradicted by findings suggesting that socioeconomic status and level of poverty are far more causative of low birth weight and poor developmental outcome than use of the substances themselves. This doesn’t imply that use of cannabis or other substances during pregnancy has no adverse effect, but does give weight to the idea that the risks have been overestimated and overemphasized due to politics and anti-drug bias.

Marijuana and Infertility: What You Need to Know

For decades, there has been an ongoing discussion regarding cannabis and infertility. Numerous anecdotal outlets have cited decreased fertility rates among cannabis users (especially a decline in sperm count in males), but is there any clinical or scientific evidence to back up these claims?

In this article, we discuss relevant contemporary research relating to the topic. We’ll also discuss whether “marijuana infertility” is truly a concern. Read on to find out more.

Does Marijuana Cause Infertility?

There is a body of evidence suggesting that marijuana causes infertility. However, even more concerning is relatively recent research that suggests that fertility, especially in males — may be declining overall.

A study published in Human Reproductive Update in 2017 identified a potentially key issue. It looked at 7,500 studies performed from 1973 to 2011. The researchers found that men from Australia, New Zealand, Europe, and North America had an almost 60% decline in sperm count. They also had a sperm concentration decline of 52%.

Researchers offered several hypotheses attributed to the decline in semen quality. These include:

  • Increase exposure to pesticides
  • Meta-changes in diet
  • Smoking
  • Exposure to higher-temperature climates
  • Meta-changes in Body Mass Index (BMI)
  • Other lifestyle/environmental factors

A major underlying concern, particularly given evidence that cannabis use is on the rise (as well as evidence that smoking tobacco affects fertility), is whether or not marijuana causes infertility. Another is whether cannabis use may have a variable impact on males’ and females’ fertility and reproduction potential.

Potential Impact of Cannabis Use on Female Fertility

Data regarding the relationship between female infertility and marijuana use is limited. However, a study published in the Journal of Women’s Health in 2016 suggests that smoking cannabis can delay a woman’s ovulation by several days.

Furthermore, a separate study published by the National Institute on Drug Abuse suggests that cannabinoids can alter hormone secretion related to reproductive function. Authors suggest that cannabinoids, specifically THC, can “inhibit secretion of LH, FSH, [and] prolactin,” resulting in “decreases in sex steroid hormones [as well as] changes in ovulation.”

However, the researchers observed that these effects are reversible when cannabis use is ceased.

Still, most experts recommend that pregnant women and women who are considering becoming pregnant – avoid the use of cannabis altogether both during and before pregnancy. This recommendation is more pressing than ever, as cannabis use among young reproductive-aged women is rising.

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In fact, according to currently available statistics, upwards of 8% of non-pregnant reproductive-aged women use cannabis on a relatively consistent basis. As authors of the above publication observe, “prenatal marijuana exposure [can be] associated with poor offspring outcomes,” including an increased prevalence of conditions like low birth weight and impaired brain development.

What About Male Fertility? Does Cannabis Reduce Sperm Count?

Another pressing concern – and an ongoing topic of debate circulating for decades – is whether or not marijuana can cause male infertility.

A study published in the American Journal of Epidemiology in 2015 appears to suggest that it can. The study observed over 1,200 Danish men aged 18-28, 45% of which had smoked cannabis in the previous three months. Twenty-eight percent of study participants used marijuana more than once a week. The study discovered that those who used cannabis regularly had a 29% reduction in sperm count.

The answer may shock you!…

However, a study published in Human Reproduction in 2019 appears to contradict the research above. This study, which took place over 17 years from 2000 to 2017, examined 1,100 semen samples from male patients enrolled in the Massachusetts General Hospital Fertility Center. The study found that cannabis users had a higher sperm count per milliliter of ejaculate (62.7 million sperm compared to 45.4 million in non-cannabis users). Only 5% of cannabis-using test subjects had sperm count levels considered low (below 15 million per milliliter).

Based on the availability of contemporary research data, the impact of cannabis use on male fertility is still largely inconclusive.

Additional Research on Weed and Infertility

Another interesting publication on the broader topic of weed and infertility appeared in 2018 in the peer-reviewed academic journal Fertility and Sterility.

In the study, researchers analyzed nearly 2,000 male and female participants that were trying to conceive. Eleven-and-a-half percent of women admitted to using cannabis during this period, along with 16.5% of men. The study results suggested that cannabis use did not have a negative impact on the time it took for couples to become pregnant.

Again, however, it is highly recommended that cannabis use be avoided among individuals trying to conceive.

Bottom Line on Marijuana and Infertility

The general discrepancy in the observations made from these above-referenced studies means we can’t draw any firm conclusions regarding the ongoing debate of marijuana and infertility. Without a doubt, more research needs to be done on the topic.

Unfortunately, there are still challenges associated with carrying out quality cannabis-based research.

At present, cannabis is only fully legal (on a national level) in Canada and Uruguay. This means that federal research funding for cannabis studies is still difficult for many global research organizations.

Regardless of whether or not marijuana causes infertility, it is best to avoid the consumption of cannabis altogether for those trying to conceive. Likewise, pregnant women should always steer clear of any form of cannabis use.