Does smoking marijuana affect fertility?

The question of how marijuana affects fertility in men and women is becoming more important as state-level legalization spreads.

It is, of course, well established that cigarette-smoking is bad for fertility, especially female fertility. It is also bad for babies, resulting in lower weights and potential long-term adverse effects. Paradoxically, relatively little is known about the effects of marijuana on fertility. With legalization of marijuana sales in increasing numbers of U.S. states, there is also increasing evidence of rapidly growing marijuana use by mothers in pregnancy.

While effects of marijuana on the fetus are not well understood, they, likely, are not favorable. Preliminary data, indeed, do suggest long-term effects on the brain of newborns. Professional organization, therefore, have come out very clearly with statements that strongly recommend against marijuana use by mothers during pregnancy.

Marijuana plant. Photo by Rick Proctor via Unsplash.

As a principle issue, it is important to be aware of the rather paradoxical contradiction that the world over the last two decades has successfully restricted cigarette smoking; yet, at the same time smoking of marijuana joints has for all practical purposes been encouraged in the U.S. (and elsewhere) by legalization of marijuana. In the U.S., legalization has occurred in many states but not yet at the federal level. Physiologic and medical consequences of inhaled tobacco and marijuana smoke, of course, differ to significant degrees. Nobody has been able to attribute healing effects to tobacco smoking; yet, marijuana, unquestionably, does have such effects and, therefore, must be viewed very differently.

But the fact that marijuana may have beneficial medical effects in certain clinical situations does not mean marijuana is safe in pregnancy and/or for women and men who are trying to establish a pregnancy. The best analogy are many fully FDA-approved medications with often lifesaving attributes which, nevertheless, are considered contraindicated in pregnancy and during conception periods and, therefore, should not be used in pregnancy or even while attempting to conceive.

The main reason is the so-called endocannabinoid system in our bodies. Tetrahydrocannabinol (THC), which is the psychoactive substance in marijuana, acts on receptors of the endocannabinoid system, which can be found widely distributed through our bodies and in especially high density in tissues of reproductive organs in women and men. There they play important roles in reproductive endocrinology through control of hormone secretion and, therefore, reproductive success.

In males, THC, thus, has been demonstrated to reduce sperm counts, though at least one recent clinical study not only was unable to demonstrate such an effect but, actually, suggested the opposite. These opposing results, however, are not necessarily contradictory because, when it comes to reproductive success, evolution has created multiple redundancies for most functions in order to guarantee maintenance of the species. Therefore, simple-minded univariant statistical analyses that do not consider other variable factors that in circumferential ways may affect results, may be misleading.

Because female fertility is even more complex, assessments of marijuana effects are even more complicated and research has, unfortunately been very limited. At least one study suggested that marijuana use may affect ovulation (release of eggs), an essential step in female conception.

There is consensus in the fertility field that, simply based on the wide distribution of endocannabinoid receptors in reproductive organs, there must be significant effects of THC on reproduction. With increasing consumption of marijuana especially in the reproductively most active age groups (and not only through smoking), one, therefore, can assume significant effects on fertility. Those, though, do not necessarily have to be exclusively negative. One, indeed, can hypothesize that, at least some, in selected populations, may also be potentially beneficial. For example, some have suggested that marijuana may improve sleep and/or reduce stress for infertile couples.

All of this is, however, currently still only a wild guessing game. Recommended responsible behavior for couples trying to achieve pregnancy, therefore, must be to abstain from marijuana use during conception periods and for women, of course, during pregnancy.

One final thought: Currently available marijuana is significantly more potent than marijuana used 20 or 30 years ago. Even relatively minor exposure, therefore, can result in significant THC levels and, consequently, receptor activation. CHR, therefore, recommends complete abstinence from all social drugs during fertility treatments, including marijuana.

This is a part of the October 2019 CHR VOICE.

Norbert Gleicher, MD, leads CHR’s clinical and research efforts as Medical Director and Chief Scientist. A world-renowned reproductive endocrinologist, Dr. Gleicher has published hundreds of peer-reviewed papers and lectured globally while keeping an active clinical career focused on ovarian aging, immunological issues and other difficult cases of infertility.