Cannabis and Pregnancy

With the legalization of recreational cannabis in many places across the world, we anticipate more women will be using and self-reporting cannabis use during pregnancy.

The prevalence of cannabis use during pregnancy ranges from 3 – 30%. Many women cite medical reasons for prenatal cannabis use such as, nausea and vomiting, anxiety, and chronic pain.

Does cannabis affect fertility and/or pregnancy?

We know that drinking and smoking during pregnancy are ill advised. But what about cannabis?

I would like to start by saying that more research is needed to understand all the potential effects of cannabis on fertility, pregnancy, breastfeeding and the offspring.

Now, the truth is that most of the recommendations proposed by physicians are based on outdated, incomplete, or simply assumptions due to lack of research and overall lack of understanding on the subject.

The current stance on the subject by the Society of Obstetricians and Gynaecologists of Canada is:

  • Pregnant women and women of child-bearing age be asked periodically about substance use, including cannabis.
  • Healthcare providers should advise pregnant women to abstain from or reduce cannabis use during pregnancy to prevent negative long-term cognitive and behavioral outcomes for exposed children.

Cannabis and male fertility

Recent study published on February 6, 2019 in the journal Human Reproduction by a group from the Chan School of Public Health in Harvard, contradicts much of what we’ve heard before. That cannabis can in fact increase men’s sperm count. This was a longitudinal study conducted over 17 years, in which 667 men enrolled at a fertility clinic in Boston. Interestingly, sub-fertile men who had previously, or currently smoked cannabis demonstrated a significantly higher sperm count and concentration, than men who had never consumed cannabis. This contradicts previous studies primarily conducted in animals which suggested an opposite effect. Studies like these must always be replicated to ensure this is a real effect, but it does prove promising. Especially because it supports the established role of the endocannabinoid system in spermatogenesis.

Another interesting finding of this study was that among cannabis smokers, greater use was associated with higher testosterone levels. Again, this is interesting because it contradicts much older studies that find cannabis use decreases testosterone in animals and humans.

The researchers do caution about what this all means, considering some of the potential study limitations. For example, cannabis use may have been under-reported because during most of the study period it was illegal. Also, they don’t know how these findings may apply to the general population, as the study was conducted with sub-fertile men in couples seeking treatment in a fertility center. Additional, studies will be needed to support these observations, but it is quite promising for the worried cannabis smoking men of the world that wish to start families soon.

Cannabis and female fertility?

In women, a study published in January 2018 in the Journal of Epidemiology and Community Health found that the probability of getting pregnant after 12 menstrual cycles was the same for women that had used cannabis and those who had not. Controlling for multiple variables, including frequency of intercourse (which was shown to be higher among the cannabis users!).

Human studies in this area show conflicting results. Some studies show cannabis causes adverse effects on reproductive hormones, semen quality, and ovulation. While other studies show no impact. Much of the research against the use of cannabis during pregnancy, comes from older more dubious studies. More recent work on the subject, seem to show that cannabis is not as bad as previously thought.

Despite this, most healthcare professional still advise against the frequent use of drugs or mind-altering substances during pregnancy. Of course, as with everything moderation is key. The same way that one glass of wine won’t sacrifice your chances of having a health child, one joint or brownie won’t either. It’s clear that in light of a significant knowledge gab with the medical field and cannabis, many biases and old-fashioned ideas remain.

Is cannabis safe to use while pregnant?

More recent studies have begun to shed light on this topic. For example, a systematic review of 31 clinical studies conducted between 1982 – 2015 published in the journal Obstetrics & Gynecology, assessed the risks involved with cannabis. The study concluded that cannabis does not pose a risk to pregnant women or their fetuses.

This supports the observations from a similar study conducted in 2010, by an international collaboration with the US Center for Disease Control (CDC). This epidemiological study looked at mothers who delivered infants between 1997 and 2004 and completed interviews for the National Birth Defects Prevention Study (n = 5871). Controlling for demographic and social factors, a multivariable linear and logistic regression found that cannabis use was not associated with decreased birth weight or preterm delivery. Interestingly, they found that in pregnant illicit drug users with low education and income, it was primarily a lack of folic acid use during the preconception that lead to problems with the baby. These patients were also most likely to have used alcohol and tobacco throughout the gestational period.

…the truth is that most of the recommendations proposed by physicians are based on outdated, incomplete, or simply assumptions due to lack of research and overall lack of understanding on the subject.

Although this is a very complicated issue, some experience physicians do currently prescribe cannabis to help treat and manage morning sickness. If you are recently pregnant and you or your doctor is interested in exploring this option with you be reassured that potentially adverse effects to your child would be unlikely.

What about during labor or after giving birth?

Whether cannabis is effective and safe during labor is still up for contention. As the few studies performed on this specific topic are inconclusive or poorly done. Yet, when presented with a diverse cocktail of drugs (anti-emetics, opioid analgesics, local anesthetics, etc) typically administered during childbirth the addition of cannabis may be an inconsequential. Although not a powerful analgesic, cannabis could be useful as a mild pain reliever or component to help distract the mother from painful contractions prior to arriving at a hospital or birthing center. Until more research is done, we cannot conclusively recommend the use of cannabis during childbirth. Especially, since we don’t know how cannabis may interact with the drug cocktail that is the current gold standard. Which could have potentially risky adverse effects.

Research looking at cannabis use after childbirth, in particular during breast feeding is also quite limited. Almost all the research conducted on the effects of cannabis on offspring come from animal studies looking at THC exposed mice. The mouse pups demonstrated significantly less weight gain and some cognitive delays. It must be said that the doses given to the mouse mothers were about 300 times higher than a human mother would consume. Other studies using mouse models have suggested a decrease in the quality of milk produced and mild sedation in pups. Yet, form these studies it is very difficult to extract conclusions applicable to humans.

Is cannabis safe during breast feeding?

One of the few studies that has carefully looked into the presence and concentration of cannabinoids in breast milk was published in the journal Pediatrics in 2018 from a lab at the University of California in San Diego. They tested the breast milk of 54 women who consumed cannabis and were lactating a child. Of those 34 (63%) had detectable THC levels and only 9% had detectable CBD levels. Levels of THC remained detectable in the samples for ~6 days after cannabis consumption. This means, we know conclusively that THC and other cannabinoids are transferred to breast milk. Now whether or not this indicates that the child is affected pharmacologically is another story. This remains to be seen, but physicians non-the-less express caution.

Check out our Cannabis Science Podcast episode on the topic of Cannabis & Pregnancy


Nassan, F.L., et al. Marijuana smoking and markers for testicular function among men from a fertility centre. Human Reproduction. 2019. pp. 1-9.

van Gelder M.M.H.J., et al. Characteristics of pregnant illicit drug users and associations between cannabis use and perinatal outcome in a population-based study. Drug and Alcohol Dependence. 2010. pp 243-247.

Wise LA., et al. Marijuana use and fecundability in North American preconception cohort study. Journal of Epidemiology and Community Health. 2018. pp 208-215

Bertrand KA., et al. Marijuana Use by Breastfeeding Mothers and Cannabinoid Concentrations in Breast Milk. Pediatrics. 2018.  

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