Men who smoke marijuana may have higher sperm counts than those who have never used the drug, a surprising new study suggests.
The findings are “not consistent” with previous research, which has suggested that marijuana has a harmful effect on men’s testicular function, the researchers said.
However, the study, published in the Feb. 6 issue of the journal Human Reproduction, doesn’t mean men should start smoking pot to up their sperm counts.
The findings are far from conclusive, and more research is needed to understand whether smoking marijuana could indeed, at certain levels, have a positive effect on sperm production.
But the study does highlight how little researchers know about the effects of marijuana on reproductive health, study senior author Dr. Jorge Chavarro, an associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health in Boston, said in a statement. “We know a lot less than we think we know.”
Marijuana and sperm
Previous studies had suggested that smoking marijuana may lower a man’s sperm count, especially among heavy users. For example, in 2015, researchers from Denmark found that men who smoked marijuana more than once per week had sperm counts that were nearly 30 percent lower than those who didn’t smoke marijuana, or those who used the drug less frequently.
However, the effects of more moderate marijuana use on sperm counts among men is less clear.
In the new study, the researchers analyzed information from 662 men who, along with their partners, were evaluated for infertility from 2000 to 2017 at the Massachusetts General Hospital Fertility Center. The men answered survey questions about how often they smoked marijuana or used other drugs, and they also provided sperm and blood samples.
Overall, a little over half of the men (55 percent) reported ever smoking marijuana in their lifetimes, and 11 percent said that they currently smoked marijuana.
The researchers found that men who reported ever having smoked marijuana had an average sperm concentration of 63 million sperm per milliliter of semen, compared with 45 million sperm per milliliter of semen among those who had never used marijuana. The findings held even after the researchers took into account some factors that could have affected sperm concentration, such as age, cigarette smoking and alcohol use.
What’s more, only 5 percent of the marijuana smokers had lower-than-normal sperm concentrations — that is, lower than 15 million sperm per milliliter of semen. Among men who never smoked marijuana, 12 percent had lower-than-normal sperm concentrations.
Among men who had ever smoked marijuana, those who used it more often had higher testosterone levels than those who used it less often.
Interestingly, each additional year that had passed since a man last used marijuana was tied to a slight increase in sperm count.