A new study suggests it does—but not in the way you might think.
Harvard researchers were surprised to find that men who have smoked marijuana had better sperm counts than their counterparts who had never used cannabis—but scientists are cautioning that the link does not mean there is a causal connection between smoking marijuana and increased fertility.
A study published this week in the journal Human Reproduction found that men who had smoked marijuana at some point in their lives had higher sperm counts, which is associated with increased fertility.
Researchers examined 1,143 semen samples from 662 men, all of whom were undergoing fertility treatments with their partners at the Massachusetts General Hospital Fertility Center.
“Men who had ever smoked marijuana had significantly higher sperm concentration than men who had never smoked marijuana,” study authors wrote. There was no difference in sperm count between current and previous marijuana smokers.
These findings came as a surprise, since previous research has indicted that smoking marijuana had a negative effect on fertility. A 2015 study found that men who smoked weekly had a lower sperm count than those that did not, and a study published in 2018 found that THC can change the structure of sperm.
Researchers said that it’s possible that low-level exposure to cannabis could aid fertility by stimulating the endocannabinoid system in the brain. However, they said that it’s just as likely that testosterone levels affect both the likelihood that a man uses cannabis (a risk-taking behavior) and his sperm production.
“Our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviors, including smoking marijuana,” Dr Feiby Nassan, who was involved with the research, told Bloomberg.
Allan Pacey, professor of Andrology at the University of Sheffield in Britain, said that men who are trying to have a child should continue to avoid cannabis.
“As the authors point out, men with higher sperm concentrations are likely to have more testosterone in their bodies and thus may be more likely to smoke marijuana because simply they are willing to take more risks,” he said. “In conclusion, I am not convinced that this paper moves us any further forward in this debate. Moreover, nor does it give support to any apparent fertility benefits of smoking marijuana. In my opinion, this should be avoided at all costs in any couples trying to start a family.”
Lead author Dr. Jorge Chavarro said that the findings highlight the need for more research into the effects of cannabis on male fertility.
“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,” he said. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”
