In the United States, an estimated 8.4% of individuals aged 12 years and older currently use cannabis, with approximately 40% of users reporting daily or near daily use.1 In addition, estimates for 2014 show that 4.2 million Americans met the criteria for cannabis use disorder.1 Rates of cannabis use are especially high among men and women of reproductive age, and will likely increase with expanded legalization of cannabis across the United States.1,2
Among other concerns related to these trends, experts point to adverse effects on fertility as a potential issue that warrants attention. For example, a 2015 study found a 29% reduction in total sperm count (95% CI, -46% to -1%) and a 28% reduction in sperm concentration (95% CI, -48% to -1%) in men who had smoked cannabis more than once per week in the prior 3 months.3
In women, research findings have shown delayed ovulation (average of 1.7-3.5 days; P =.04) in those who had smoked cannabis at least once in the prior 3 months compared with control individuals.4 In addition, although cannabis smokers made up only 15% of this study population, 43% of anovulatory cycles that occurred during the study were observed in this group.
In terms of ability to conceive, recent survey data5 suggest that “smoking marijuana, ranging from less than once per month to daily, in either partner does not significantly affect time to pregnancy,” according to the authors of a brief review published in 2019 in CMAJ.6 “However, for couples with infertility, the changes in ovulatory function and sperm count associated with smoking marijuana could compound their difficulty with conceiving.”
Nevertheless, there is a dearth of human research in this area, in which most of the current data were derived from small observational studies, and results have been conflicting or inconclusive overall.
To learn more about the available evidence and clinical implications pertaining to cannabis use and fertility in men and women, Endocrinology Advisor checked in with the following experts who have conducted research in this area: Sara Ilnitsky MD, FRCSC, a physician and researcher at the University of Alberta who coauthored the 2019 CMAJ review; Raul I. Clavijo, MD, assistant clinical professor in the Department of Urologic Surgery at the University of California, Davis, School of Medicine; and Sandeep Raha, PhD, MSc, associate professor in the Department of Pediatrics at McMaster University.
Endocrinology Advisor: What is known thus far about the effects of cannabis on fertility, and what are believed to be the underlying mechanisms?
Sara Ilnitsky, MD, FRCSC: Tetrahydrocannabinol (THC) is a highly lipophilic compound within the cannabinoid family. Cannabinoids are found in nature, specifically in cannabis plants, but they are also synthesized endogenously as part of the endocannabinoid system. The endocannabinoid system is found in many reproductive tissues including ovarian follicles, fallopian tubes, and endometrium in women; the testis, vas deferens, and sperm cells in men; and the anterior pituitary in both women and men. We also know that this system is involved in embryo transport through the fallopian tube and implantation in the uterus. The endocannabinoid system maintains a tenuous, tissue-specific balance of cannabinoid concentrations, and therefore, biological effects. It is therefore plausible that disrupting this system with THC or other cannabinoids could affect fertility.7