Marijuana smoking may be linked with having higher sperm concentrations

(Matilde Campodonico/Associated Press)

Turns out marijuana could actually have significant benefits for the reproductive health of men.

In a new study published Tuesday, researchers at the Harvard T.H. Chan School of Public Health found that men who smoke marijuana — or once did — “had significantly higher concentrations of sperm when compared with men who have never smoked marijuana,” according to a statement from the school.

“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,” Jorge Chavarro, associate professor of nutrition and epidemiology at Harvard Chan School, said in the statement. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”


If you’re surprised, don’t worry — you’re not alone.

Previous studies on the effects of marijuana use on reproductive health have largely shown negative outcomes, though “those studies had focused on animal models or on men with histories of drug abuse,” Harvard said.

Nonetheless, researchers this time around hypothesized along those lines, predicting that marijuana use would be linked with worse semen quality.

Instead, they found the opposite.

The researchers collected 1,143 semen samples from the Fertility Center at Massachusetts General Hospital between 2000 and 2017 from 662 men, 55 percent of whom reported smoking marijuana at some point in their lives. About 11 percent of the marijuana consumers reported that they currently smoke.

On average, the men who reported smoking marijuana had 62.7 million sperm per milliliter of ejaculate, while the nonsmokers had an average of 45.4 million sperm per milliliter.

A normal concentration can range from 15 million to 200 million sperm per milliliter, according to the Mayo Clinic. Twelve percent of nonsmokers were below that threshold in the study, compared to only 5 percent of marijuana smokers.


Among marijuana smokers, researchers also found that more marijuana use was linked to higher testosterone levels.

The researchers in the study cautioned that they aren’t sure how their results would apply to the general population.

“Our findings were contrary to what we initially hypothesized. However, they are consistent with two different interpretations, the first being that low levels of marijuana use could benefit sperm production because of its effect on the endocannabinoid system, which is known to play a role in fertility, but those benefits are lost with higher levels of marijuana consumption,” said Feiby Nassan, lead author of the study.

“An equally plausible interpretation is that our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviors, including smoking marijuana.”

Felicia Gans can be reached at felicia.gans@globe.com. Follow her on Twitter @FeliciaGans.