Study Links Cannabis Use to Higher Sperm Counts

New research from scientists at Harvard could disprove a commonly-held belief about cannabis consuming males.

Good news for marijuana users: New research suggests the use of cannabis not only has no adverse effect on male fertility, but that it may also help to improve it. A new study published in the journal Human Reproduction has found that men who have smoked marijuana at some point in the past had significantly higher sperm concentrations when compared to men who hadn’t.

Researchers from the Harvard T.H. Chan School of Public Health also found no significant difference in sperm count between current consumers of marijuana and former marijuana smokers.

The findings contradict with conclusions in some previous research, which have linked marijuana use to negative effects on sperm and male fertility. The researchers in the new marijuana’s effect on sperm study went into their investigation hypothesizing that marijuana smoking would lead to a lower sperm count and worse semen quality.

“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, one of the study’s researchers and associate professor of nutrition and epidemiology at Harvard Chan School, 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.”

To study marijuana’s effects on sperm, Chavarro and his colleagues analyzed 1,143 semen samples collected from more than 650 primarily white, college educated men with a mean age of 36 between 2000 and 2017. Three hundred and seventeen of the men also provided blood samples, used to measure reproductive hormones.

The men who reported having smoked marijuana before had an average sperm concentration of 62.7 million sperm per milliliter of semen. Those who had never used marijuana in the past had a sperm concentration of 45.4 million sperm per milliliter, or 28 percent less.

Only 5 percent of marijuana smokers had sperm concentrations below the World Health Organization’s threshold for “normal.” Of never-smokers, 12 percent had sperm counts below the “normal” threshold.

Marijuana on Male Fertility - Image of Man Hiking

Potential Roles of Endocannabinoid System and Testosterone

The researchers in the marijuana’s effects on sperm study presented two potential explanations as to why men who had used marijuana in the past would have higher concentrated semen.

The first is that low levels of marijuana could elicit positive effects on sperm production through its interaction with the body’s endocannabinoid system, a self-regulatory network known to play a role in fertility. Cannabinoids, a class of compounds found in marijuana, interact with the endocannabinoid system through cannabinoid receptors, found throughout the body.

Tetrahydrocannabinol (THC), one of the major cannabinoids found in marijuana, was found in 2017 to have no negative effects on male reproductive processes.

The second potential explanation for marijuana’s effects on sperm could be related to cannabis smokers having naturally higher levels of testosterone. Blood samples collected revealed that among marijuana smokers, greater use was associated with higher testosterone levels.

“Our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviors, including smoking marijuana,” said Feiby Nassan, the study’s lead author and a postdoctoral research fellow at Harvard Chan School.

The new study, “Marijuana smoking and markers of testicular function among men from a fertility centre,” is available to access online through Oxford Academic.

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