Cannabis and Fertility: Five Things Scientists Want You to Know

Thanks to waves of legalization and a strong association with the medical and wellness industries, scores of women are now using cannabis to relieve their morning sickness symptoms. But, unsurprisingly, doctors are warning that “toking for two” isn’t the healthiest activity for a developing fetus. 

Now, writing in the Canadian Medical Association Journal, two researchers have presented five “things to know” about cannabis and fecundity to better inform doctors and prospective cannabis-using parents about the drug’s fertility risks.

“Legalization will likely increase marijuana use among reproductive-age men and women,” said Dr Ilnitsky, a co-author of the paper and a reproductive endocrinology and infertility fellow at Western University in London, Ontario. “So we wanted to help inform health care providers of what we do and do not know about marijuana’s effect on fertility.”

Speaking on the CMAJ’s podcast, Dr Ilnitsky discussed the pharmacology of THC, how cannabis can affect fertility, and how the effect is different in women compared to men. “We know that [the endocannabinoid system] is involved in embryo transport through the fallopian tube and implantation in the uterus,” she explained. 

“And the endocannabinoid system maintains a tenuous tissue-specific balance of cannabinoid concentrations and, therefore, biological effects. So I think it’s plausible that disrupting this system with THC or other cannabinoids could affect fertility.”

Ilnitsky’s “five things to know” about cannabis and fertility are as follows:

1. The active ingredient in marijuana, tetrahydrocannabinol (THC), acts on the receptors found in the hypothalamus, pituitary and internal reproductive organs in both males and females.
2. Marijuana use can decrease sperm count. Smoking marijuana more than once a week was associated with a 29 percent reduction in sperm count in one study.
3. Marijuana may delay or prevent ovulation. In a small study, ovulation was delayed in women who smoked marijuana more than 3 times in the 3 months before the study.
4. Marijuana may affect the ability to conceive in couples with subfertility or infertility but does not appear to affect couples without fertility issues.
5. More, and better quality, research is needed into the effects of marijuana on fertility.

All five guidelines are founded in scientific studies and paralleled in the policies of leading fertility authorities. The American College of Obstetricians and Gynecologists, for example, advises all doctors to test their pregnant patients for cannabis use and encourage them to quit, whether they use it for medical purposes or not. 

Of course, not all five points are completely agreed upon by every relevant scientific study. For example, some research papers have given contrary conclusions on male fertility. One study conducted by the Harvard TH Chan School of Public Health concluded that men who have smoked marijuana at some point in their life had significantly higher concentrations of sperm than men who have never smoked the substance. 

However, a lead author of the study did clarify that “an equally plausible interpretation is that our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviors, including smoking marijuana.”

When asked for the advice she’d give to would-be parents using cannabis for therapeutic purposes during the CMAJ's podcast, Dr Ilnitsky replied, “I think it depends on what the indication is medically and I think it would be a risk-benefit decision with their physician and an informed discussion about what the risks are and if those risks are worth taking while trying to get pregnant and once in pregnancy.” 

“So it’s a discussion we would have with any medication that isn’t as well studied in pregnancy as we’d like it to be.”