The devastation of infertility reaches across all social and income levels, causing pain, stress, and frustration as well as time and money. About 15 percent of couples are affected nationally, costing the US health-care system more than $5 billion a year.
Marijuana is one of the most widely used recreational drugs among people of reproductive age. Given the costs of infertility, identifying its modifiable risk factors, such as recreational drug use, is an important public health goal. According to a new study led by School of Public Health researchers, marijuana use—by either men or women—does not appear to lower a couple’s chances of being able to conceive.
The study, published in the Journal of Epidemiology and Community Health, is the first to evaluate the link between fecundability—the average probability of conception in a given month of regular intercourse—and marijuana use.
From 2012 to 2013, marijuana use among adults 18 years and older in the United States was 6.9 percent for women and 12.3 percent for men. Canada also has a high rate of marijuana use, with about 7 percent of women and 14 percent of men 15 years or older using marijuana in 2013. Previous studies examining the effects of marijuana use on reproductive hormones and semen quality have come up with conflicting results.
“Given the increasing number of states legalizing recreational marijuana across the nation, we thought it was an opportune time to investigate the association between marijuana use and fertility,” says lead author Lauren Wise, an SPH professor of epidemiology. “We scoured the literature and noticed that there were no studies of the effects of marijuana use on fecundability, the probability of conception in a given month of regular unprotected intercourse. Our study sought to fill an important gap in the literature.”
In SPH’s Pregnancy Study Online (PRESTO), a web-based prospective cohort study of North American couples, the researchers surveyed 4,194 women from 21 to 45 living in the United States or Canada. The study specifically targeted women in stable relationships who were not using contraception or being treated for infertility. The women completed an online baseline questionnaire and were given the option to invite their male partners to participate; 1,125 of these men enrolled. The women completed follow-up questionnaires every 8 to 12 weeks, so the researchers could learn if they became pregnant.
The researchers were able to assess the frequency of marijuana use by asking participants, on the baseline questionnaire, about its use during the previous two months, with response options of “every day,” “4-6 times per week,” “1-3 times per week,” and “less than 1 time per week.” They also asked about factors that could potentially affect their findings, such as age, residence, race or ethnicity, education, use of multivitamin supplements, height, weight, smoking history, exposure to environmental tobacco smoke, physical activity, alcohol consumption, caffeine intake, soda intake, reproductive history, intercourse frequency, history of sexually transmitted infections, history of physician-diagnosed medical conditions, employment status, average hours worked a week, average duration of sleep during the previous month, perceived stress, and depressive symptoms.
The researchers found that during the period from 2013 through 2017, approximately 12 percent of the women participating and 14 percent of the men participating reported marijuana use in the two months before completing the baseline survey. After 12 cycles of follow-up, probability of conception was similar among couples who used marijuana and those who did not.
“Given that half of pregnancies in the USA are unintended, our results may not apply to couples not actively trying to conceive,” Wise says. “Nevertheless, marijuana use did not differ markedly by intensity of trying to conceive, as indicated by the similar proportions of couples doing something to improve their chances of conception.”
The researchers stress that questions about the effects of marijuana use remain. As one example, they note the challenges in classifying people correctly according to the amount of marijuana used, especially when relying on self-reported data. Moreover, the study focused on marijuana use in the two months prior to enrollment in the study and did not have data on duration, general patterns of use, or method of use. “Future studies with day-specific data on marijuana use might better be able to distinguish acute from chronic effects of marijuana use, and evaluate whether effects depend on other factors,” they write.
“In conclusion, our study showed no clear association between female or male marijuana use and fecundability among North American pregnancy planners,” says Wise. “The extent to which our results were attenuated by misclassification of marijuana use is unclear. Future studies with day-specific data on marijuana use might better be able to distinguish acute from chronic effects of marijuana use, and evaluate whether effects depend on other factors.”
Additional BU coauthors on the study: epidemiology doctoral student Amelia Wesselink (SPH’18), Elizabeth Hatch and Kenneth Rothman, both SPH professors of epidemiology, and Shruthi Mahalingaiah (SPH’15), an SPH assistant professor of epidemiology and a School of Medicine assistant professor of obstetrics and gynecology. Ellen Mikkelsen and Henrik Toft Sørensen from Aarhus University Hospital in Denmark were also coauthors.