Marijuana Usage Linked to Higher Sperm Counts

A surprising new study performed at Harvard might just change the way you think about your fertility. Researchers from the T.H. Chan School of Public Health found higher average sperm counts in men who use or have used marijuana at some time in the past (Chavarro). Does this mean that men who smoke marijuana are more fertile than those who have never touched it?

Back up… what did previous research say about marijuana usage and sperm?

Several past studies associated marijuana usage with poorer semen quality. In fact we did a blog post on this topic a while back! In 1990, researchers thought marijuana was linked to pyospermia, a condition in which the elevation of white blood cell counts in semen weakens the sperm and leads to damaged genetic material (Close). A Danish study also showed that regular marijuana smoking more than once per week was associated with a 28% lower sperm count. The combined use of marijuana more than once per week reduced the sperm concentration by 52%. It reduced total sperm count by 55%.

Discussion of these results concluded that THC causes improper swimming patterns of sperm. This reduces the ability of the sperm to attach to an egg during fertilization. The study also raises the possibility that marijuana use could affect sperm production via the body’s neurotransmitters (Goldberg).

The authors of Harvard’s new study expected to find that men who smoked pot would have worse semen quality.

So what does this new study tell us about how weed impacts sperm?

The Harvard team, led by Associate Professor Jorge Chavarro, analyzed health surveys and semen samples from more than 650 men seeking fertility treatment at Massachusetts General Hospital between 2000 and 2017. Of the men surveyed, 55% said that they had smoked marijuana at some point during their lives. 45% said they had smoked it in the last three months,  and 11% said they currently smoked pot.

Men who reported smoking marijuana had higher average sperm concentrations in their semen than men who h

Higher sperm concentrations were found in men who had smoked pot.

ad never smoked. They were much less likely to have abnormally low levels, the study found. Those who smoked weed at some point in their life had an average sperm concentration of 62.7 million sperm per milliliter of ejaculate. Men who had avoided marijuana entirely had mean concentrations of 45.4 million/mL.  That’s quite the difference!

Only 5% of weed smokers had sperm concentrations below the 15 million/mL, the threshold the World Health Organization has set for a “normal” sperm count. 12% of men who’d never smoked marijuana were found to be below the threshold.

Sounds like there are conflicting results. What should I do to maximize my fertility?

Higher testosterone is directly linked to higher total sperm count.

As surprising as these findings might be, the researchers do not suggest that men who are trying to maximize their fertility should smoke marijuana. The Harvard study did not prove that smoking marijuana causes higher fertility; it only found an association between the two. Chavarro says that a far more likely explanation is that men who have higher levels of testosterone are more likely to make risky decisions, such as to smoke marijuana. Men with higher levels of testosterone are also more likely to have higher sperm counts. This a phenomenon known as “reverse causation.”

The main takeaway is that in reality, we know litte about the long-term health effects of marijuana, especially on fertility. The bottom line is this: “The men who are most affected likely have naturally occurring borderline fertility potential, and the THC from marijuana may push them over the edge into infertility,” says Lani J. Burkman, Ph.D., who was the lead author on a 2002 study on hormone signaling in the human body (Schuel).  “THC remains stored in fat for a long period, so the process may be quite slow. We can’t say  that everything will go back to normal. Most men who have borderline fertility are unaware of that fact. It’s difficult to know who is at risk.”



Ducharme, Jamie. “A New Study Says Pot Smokers May Have Higher Sperm Counts. But There’s a Catch.” Time, 6 Feb. 2019,

Close, Clare E., et al. “Cigarettes, Alcohol and Marijuana Are Related to Pyospermia in Infertile Men.” Journal of Urology, vol. 144, no. 4, 1990, pp. 900–903., doi:10.1016/s0022-5347(17)39618-0.

Gundersen, Tina Djernis, et al. “Association Between Use of Marijuana and Male Reproductive Hormones and Semen Quality: A Study Among 1,215 Healthy Young Men.” American Journal of Epidemiology, vol. 182, no. 6, 2015, pp. 473–481., doi:10.1093/aje/kwv135.

Goldberg, Carey. “Surprising Harvard Study Finds Higher Sperm Counts In Marijuana Smokers.” Surprising Harvard Study Finds Higher Sperm Counts In Marijuana Smokers | CommonHealth, WBUR, 5 Feb. 2019. 

T, Buddy. “Why Marijuana Smokers Have Lower Total Sperm Counts.” Verywell Mind, Verywell Mind, 28 May 2019. 

Goldhill, Olivia. “Harvard Scientists Found a Link between Smoking Weed and Higher Sperm Count.” Quartz, Quartz, 6 Feb. 2019. 

Chavarro, Jorge, et al. Marijuana smoking and markers of testicular function among men from a fertility centre, Human Reproduction, Volume 34, Issue 4, April 2019, Pages 715–723.  

Schuel, Herbert, et al. “Evidence That Anandamide-Signaling Regulates Human Sperm Functions Required for Fertilization.” Molecular Reproduction and Development, vol. 63, no. 3, 2002, pp. 376–387., doi:10.1002/mrd.90021.