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Study Finds Marijuana Smokers Have Higher Sperm Counts, And We're Not Sure Why


Rachel Baxter

Copy Editor & Staff Writer

DFP Photographic/Shutterstock

Lawmakers have become a lot more chill about marijuana recently. Many people assume this means the drug is totally safe to use, but scientists are still working out exactly what it does to our bodies. Now, researchers at Harvard have found an unexpected side effect of smoking pot – it appears to increase sperm count.

A team led by the Harvard T.H. Chan School of Public Health collected 1,143 semen samples from 662 men between 2000 and 2017. The average age of the volunteers was 36, and they were asked whether they had ever smoked more than two joints or the equivalent amount of marijuana in their lives, and if they were current smokers.


Fifty-five percent of the men said they had smoked marijuana at some point, with 44 percent doing so in the past and 11 percent being current users.

To their surprise, the researchers found that marijuana smokers had higher sperm counts than men who had never used the drug, an average of 62.7 million sperm per millimeter compared to 45.4 million. Meanwhile, just 5 percent of marijuana smokers had sperm counts below the level considered normal by the World Health Organisation, whereas 12 percent of non-smokers did.  

The researchers also took blood samples from 317 of the men to assess their hormone levels and found that marijuana smokers had higher levels of testosterone. The research is published in the journal Human Reproduction.

While the findings are certainly intriguing, it’s important to note, as the researchers do, that the study is not without its limitations, and the results certainly don’t mean that marijuana is great for your reproductive health – previous research has linked it to reduced fertility, after all.


“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,” explained study co-author Jorge Chavarro 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.”

The participants in the new study self-reported their marijuana use, so the details they gave may not have been accurate. What’s more, all the of the men were enrolled at a fertility clinic, meaning they were seeking medical help with their partners to try to get pregnant. They were also all college-educated white men, so the results can’t be applied to the wider population.

Another issue with the study is that it doesn't compare regular marijuana users to non-users, it simply compares non-users to people who have used the drug at some point in their life. Therefore, it could be that men who naturally have more testosterone and higher sperm counts are more likely to take risks and give marijuana a try. 

“Our findings were contrary to what we initially hypothesized,” said lead author Feiby Nassan. “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.


“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.”

The team concludes in their paper that moderate marijuana use may improve testicular function, but that this likely reverses at high doses resulting in “adverse effects”. So no, smoking pot all day won’t give you super sperm, but small amounts may have some benefit. We need more research to find out.


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