A new study out of Harvard might complicate the narrative around marijuana’s potential health risks, at least when it comes to men’s fertility. It found that men who reported ever using cannabis actually had higher sperm counts on average than men who claimed to have never touched the stuff. Male cannabis users were also less likely to have unhealthy sperm counts than teetotallers.
More than one study (including one last December) has suggested that cannabis could lower men’s sperm counts or otherwise negatively affect their reproductive health. But many of these studies have only involved animals or focused on a small group of people (including the one last December). There’s also been conflicting evidence showing that pot use among men and women has no effect on a couple’s chances of conceiving.
In the latest study, published Tuesday in Human Reproduction, researchers at the Harvard T.H. Chan School of Public Health and elsewhere looked at a specific group of men: fertility clinic patients.
They looked at semen samples taken from more than 600 men in the US who had visited Massachusetts General Hospital’s fertility clinic from 2000 to 2017. Along with their medical history, the men were also asked if they had ever used cannabis and, if they had, whether they were still using it. About half of the men in the sample had also gotten a blood test, allowing the researchers to look at their levels of hormones such as testosterone.
Just over 50 per cent of the men reported using cannabis; half of these men reported using it in the past, while 11 per cent said they were current users.
To the researchers’ surprise, though, the cannabis users had noticeably higher sperm counts on average (62.7 million sperm per millilitre of semen) than did the men who said they never used cannabis (45.4 million sperm per millilitre of semen). And while 12 per cent of non-tokers had a low sperm count (15 million sperm per millilitre of semen or less), the same was true for only 5 per cent of cannabis users. The pattern was the same regardless of past or current cannabis use.
“These unexpected findings highlight how little we know about the reproductive health effects of marijuana, and in fact of the health effects of marijuana in general,” study author Jorge Chavarro, an associate professor of nutrition and epidemiology at Harvard, said in a statement. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”
There’s definitely a few caveats to take into account here. The biggest one is that the possible effects of cannabis on men visiting a fertility clinic (some of whom are likely infertile already) might not be representative of its effects on men in general. But leaving that aside, this is also an observational study, which only can show correlations between two things (cannabis and sperm counts), not prove that one causes the other. These two things might be completely unrelated to one another. Or maybe the relationship between the two is more complicated than it looks on the surface.
In this study, for instance, cannabis users were also more likely to have higher testosterone levels, which can affect sperm count. But maybe men with high testosterone are just more likely to do drugs. It’s also possible that, as some research has suggested, heavy or early cannabis use is really what can harm sperm, while the occasional puff as an adult might provide a boost to fertility.
Lastly, there’s also the reality that many men in this study might have been reluctant to admit they’ve smoked weed. So the comparison in sperm counts between reported users and non-users isn’t necessarily 100 per cent accurate.
None of these limitations or considerations invalidate study’s findings, it’s just a sign, as Chavarro said, that we need to study cannabis more (the fact that cannabis is still considered more dangerous than opioids by the US government remains a roadblock to that research, incidentally). If the study’s enough to give guys out there with a regular weed habit a sense of relief, though, so be it. But personally, I wouldn’t necessarily spring for the cannabis-enhanced lube just yet. [Human Reproduction via Harvard T.H. Chan School of Public Health]
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