Harvard: Cannabis Might Help Guys Make Babies

By Ben Grenrock on February 14, 2019

Could smoking blunts make you more fertile? According to a recently published Harvard University study: maybe.

Researchers at the Harvard T.H. Chan School Of Public Health found that men with a history of smoking cannabis had both a higher concentration of sperm and higher sperm counts than men who reported never having smoked. These unexpected findings, published in the journal Human Reproduction, might upend previous notions of how cannabis effects testicular function.

Though scientific literature on the subject is scarce, past studies that looked into how cannabis use impacts fertility indicated that smoking leads to lower sperm quality and, generally, to decreased fertility. Thus, this new information has come as a shock to the scientific community—surprising even the research team and leading it to caution against jumping to conclusions regarding the significance of their findings. 

In an interview with Time, study co-author Dr. Jorge Chavarro clarified, “This does not mean using marijuana is going to increase your sperm count.” The study only shows an association between smoking cannabis and elevated sperm counts/concentrations, he explained, and was not designed to show a causal link between cannabis use and fertility. But that association definitely does exist, holding up to a two-month round of incredulous double-checking of the data by Chavarro and his team.

The study consisted of 662 men who sought treatment at the Massachusetts General Hospital Fertility Center between 2000 and 2017. As part of a lifestyle questionnaire administered to them as fertility patients, 55 percent of the participants reported having smoked cannabis at some point in their lives. In comparing the survey data with the samples of sperm collected, the team found that cannabis users had higher sperm counts, higher sperm concentration and less quantities of FSH—a hormone that in high concentrations can lower fertility.

On paper, this data seems to challenge science’s basic understanding of how cannabis impacts fertility. However, sometimes data is just data, and the numbers may not necessarily correlate with real world truths. 

In the published paper, the researchers write that while, on the one hand, their findings show cannabis to have a positive impact on male fertility, but “on the other hand, the associations of marijuana smoking with sperm count and FSH concentrations were stronger for past smokers than for current smokers even though these two groups did not differ significantly from each other. Furthermore, longer duration since last use of marijuana was related to higher sperm count. These other results raise the possibility that our findings are not explained by a true underlying biologic mechanism but are instead spurious associations.”

The paper’s authors postulate that the link they discovered between cannabis and sperm count might have more to do with higher testosterone levels than the possibility that smoking bowls produces sperm. “Men with higher circulating testosterone concentrations are more likely to engage in risk-seeking behaviours, including marijuana and cocaine use,” the researchers explain, “and testosterone is positively related to sperm count.” Therefore, it’s possible that the cannabis users in the study simply had higher testosterone levels then their non-smoking counterparts and that's what accounts for their relative bounty of sperm.

Whether or not smoking cannabis increases fertility, this new study shows that “these findings are not consistent with a deleterious role of marijuana smoking on testicular function as initially hypothesized.” Given the conflicting results between this and past research, the only thing that is entirely clear is the need for more investigation into the physiological impact of cannabis use.

And simply increasing the number of studies conducted may not be enough. The research team took the time in their paper to note in that the negative stigma around cannabis makes it extremely difficult for scientists to study. “The most important limitation of the study is the possibility of underreporting of marijuana use given its status as an illegal drug during most of the study, its social stigma and potential effects on insurance coverage for infertility services of disclosing this information,” the researchers argued. 

Perhaps to get to the truth of cannabis’ effect on fertility and a whole host of other medical processes, societal views on cannabis will need to shift. 

Photo credit: Elena Kulikova

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