The impact of cannabis on maternity is a hugely controversial topic, with all sorts of inaccurate claims being thrown around regarding both the positive and negative effects of weed. The bottom line is that very few significant studies have been conducted into the role of cannabis in fertility, pregnancy or early motherhood, and those that do exist are generally hampered by small sample sizes and problematic methodologies. That said, research into this highly important area is slowly growing, allowing us to gain a few crucial insights into the ways in which cannabis affects reproduction in women.
Cannabis And Fertility
Given that cannabinoid receptors are present in the oviduct and uterus, it seems plausible to conclude that the endocannabinoid system plays some role in fertility and reproduction. Whether or not cannabis interferes with this, however, is a matter of much debate.
In a recent study involving 913 women, cannabis use was found to have no effect on levels of anti-Müllerian hormone (AMH), a key marker of fertility that is strongly associated with IVF success rates[i]. However, because only a very small fraction of participants in this study claimed to use weed regularly, it can’t be considered a reliable indication of the overall impact of cannabis on reproduction in women.
In a separate study, published in 2018, more than 1,000 women who were trying to conceive reported on how long it took them to get pregnant. An analysis of the data revealed that cannabis use had no impact whatsoever on the number of months required to become pregnant[ii]. This was backed up by another study that same year, which found no associated been cannabis use and fecundability, which in this case is defined as the probability of conception per menstrual cycle[iii].
It must be noted, however, that none of these studies were proper clinical trials, and relied only on self-reported cannabis use while failing to take into account other genetic, medical or lifestyle factors that may influence fertility. As such, they probably don’t tell the whole story regarding the impact of cannabis of reproduction in women.
Unsurprisingly, therefore, one can also find a number of studies that contradict these findings, including one published this year which concluded that cannabis use is associated with reduced fecundability[iv].
Cannabis And Pregnancy
It is thought that cannabinoids are able to cross the placenta and enter the foetal bloodstream, although whether or not this alters a baby’s development is a question that has not yet been definitively answered. Contradictions abound once more, and the ethical issues associated with giving cannabis to pregnant women means there we will probably never get a proper clinical study on the subject. Naturally, though, pregnant women should always be cautious about the medications and other substances they ingest – and that applies to weed too.
Several studies have suggested that using cannabis during pregnancy can negatively impact foetal development, birthweight and pregnancy outcomes, although there is very little consensus on the issue. According to one major study that came out last year, this is down to the fact that most research into cannabis use in pregnancy is faulty.
The study authors argue that there is no value in comparing babies who have been prenatally exposed to cannabis to those that haven’t, as this fails to take into account other crucial factors such as maternal health, genetics and socioeconomic background. As an alternative, they suggest using universal averages as a barometer to determine how prenatal cannabis exposure affects development.
To prove their point, they re-evaluated all of the available literature regarding cognitive performance among babies who had been prenatally exposed to cannabis. Of a total of 1,004 babies, only three fell below the normal range, suggesting that cannabis use in pregnancy probably doesn’t cause cognitive deficits[v].
In spite of this, it is worth remembering that we really don’t have enough solid research to make any definitive statements regarding the impact of cannabis on reproduction in women, so it’s advisable to err on the side of the caution – especially during pregnancy.
Cannabis And Breastfeeding
It’s well known that breast milk contains endocannabinoids such as anandamide, although the role that these compounds play in a baby’s development is not fully understood. Nevertheless, the fact that this CB1 agonist is transferred from mother to baby indicates that cannabinoids must have an important function.
When it comes to phytocannabinoids, the picture is even more unclear. Way back in the 1980s, researchers discovered that THC enters the breast milk of mothers who use cannabis regularly[vi]. More recent studies have indicated that THC concentrations in breast milk peak about an hour after use, and then decline back to baseline levels a few hours later[vii].
Because of this, some doctors recommend waiting at least two hours after smoking a joint before breastfeeding, mirroring the advice that is given for alcohol. However, a brand new study – published in March 2021 – found evidence that THC may remain in breast milk for six weeks following cannabis use, indicating that new safety guidelines may be necessary[viii].
Fortunately, it seems likely that only a small fraction of the ingested cannabinoids actually make their way into breast milk, with one study finding that about 2.5 percent of the THC consumed by a mother ends up being passed on during lactation[ix].
By now you probably won’t be surprised to hear that we don’t really know how significant all of this is for a baby’s development. However, one notable study found that cannabis use has no impact on weaning time, leading the authors to conclude that it doesn’t interfere with lactation. The same study also indicated that babies’ height, weight and locomotor activity was unaffected by maternal cannabis use during the breastfeeding years[x].
Of course, though, none of this is conclusive, and there are simply too many unknowns for us to say precisely how cannabis affects reproduction in women. At the end of the day, therefore, it really is up to each woman to make her own decisions regarding cannabis use, although hopefully this summary of the available research will help make that choice a little easier.
[i] White AJ, Sandler DP, D’Aloisio AA, Stanczyk F, Whitworth KW, Baird DD, Nichols HB. Antimüllerian hormone in relation to tobacco and marijuana use and sources of indoor heating/cooking. Fertility and sterility. 2016 Sep 1;106(3):723-30. – https://www.sciencedirect.com/science/article/abs/pii/S0015028216612827
[ii] Kasman AM, Thoma ME, McLain AC, Eisenberg ML. Association between use of marijuana and time to pregnancy in men and women: findings from the National Survey of Family Growth. Fertility and sterility. 2018 May 1;109(5):866-71. – https://www.sciencedirect.com/science/article/abs/pii/S0015028218300153
[iii] Wise LA, Wesselink AK, Hatch EE, Rothman KJ, Mikkelsen EM, Sørensen HT, Mahalingaiah S. Marijuana use and fecundability in a North American preconception cohort study. J Epidemiol Community Health. 2018 Mar 1;72(3):208-15. – https://jech.bmj.com/content/72/3/208.abstract
[iv] Mumford SL, Flannagan KS, Radoc JG, Sjaarda LA, Zolton JR, Metz TD, Plowden TC, Perkins NJ, DeVilbiss EA, Andriessen VC, AC PS. Cannabis use while trying to conceive: a prospective cohort study evaluating associations with fecundability, live birth and pregnancy loss. Human Reproduction. 2021 Jan 9. – https://academic.oup.com/humrep/advance-article/doi/10.1093/humrep/deaa355/6075089
[v] Torres CA, Medina-Kirchner C, O’malley KY, Hart CL. Totality of the evidence suggests prenatal cannabis exposure does not lead to cognitive impairments: a systematic and critical review. Frontiers in Psychology. 2020 May 8;11:816. – https://www.frontiersin.org/articles/10.3389/fpsyg.2020.00816/full
[vi] Perez-Reyes M, Wall ME. Presence of AMetrahydrocannabinol in human milk. New England Journal of Medicine. 1982;307(13):819-20. – https://www.cabdirect.org/cabdirect/abstract/19832700054
[vii] Baker T, Datta P, Rewers-Felkins K, Thompson H, Kallem RR, Hale TW. Transfer of inhaled cannabis into human breast milk. Obstetrics & Gynecology. 2018 May 1;131(5):783-8. – https://journals.lww.com/greenjournal/Fulltext/2018/05000/Transfer_of_Inhaled_Cannabis_Into_Human_Breast.5.a
viii] Wymore EM, Palmer C, Wang GS, et al. Persistence of Δ-9-Tetrahydrocannabinol in Human Breast Milk. JAMA Pediatr. Published online March 08, 2021 – https://jamanetwork.com/journals/jamapediatrics/article-abstract/2776975
[x] Tennes K, Avitable N, Blackard C, Boyles C, Hassoun B, Holmes L, Kreye M. Marijuana: prenatal and postnatal exposure in the human. NIDA Res Monogr. 1985 Jan 1;59:48-60.