Updated on January 21, 2020.
Medical content reviewed by Dr. Joseph Rosado, MD, M.B.A, Chief Medical Officer
For men who enjoy smoking a little weed, but fear it could affect their fertility, new research may help ease those concerns. A new study published in the journal Human Reproduction has found that marijuana may not be so bad after all, when it comes to men’s health. In fact, men who had smoked marijuana at some point during their lives had significantly higher sperm concentrations compared to those who had never used it.
These findings are somewhat surprising, as previous research has suggested the opposite—that marijuana use can have a negative effect on male reproductive health. In fact, in this study, which was done in patients seen at a fertility clinic, the authors had hypothesized that smoking marijuana would be associated with poorer semen quality and lower blood testosterone levels.
“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,” study author Jorge Chavarro, MD, ScD, associate professor of nutrition and epidemiology at Harvard T.H.Chan School of Public Health, said in a release. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”
Marijuana has been extensively studied, but most of the research on its effects on health have focused on its neurological impact, such as how it may affect neurocognitive functioning. But experimental studies have suggested that it can have negative effects on the male reproductive system, such as testicular atrophy, and reduced libido and sexual function. But as legal access to marijuana continues expanding across the U.S., more studies have been done to examine the effects of its active ingredient, tetrahydrocannabinol (THC), in diverse populations that include teens, adults and pregnant women. One study conducted last year, for example, looked at how marijuana use could affect the male reproductive system in both rats and humans, and results showed that it caused genetic changes in sperm. However, it was not clear what effect those changes could have, or if they would be passed along to any offspring. The researchers cautioned that men should abstain from marijuana when trying to conceive a child, to be on the safe side.
However, another study from 2018 looked at marijuana use in both men and women and found that it did not appear to have any impact on the ability to conceive a child. There was no association between marijuana use or the frequency of use, and time to pregnancy among men and women.
In the Human Reproduction study, marijuana didn’t appear to be detrimental to male reproductive health. While research has suggested that smoking marijuana can adversely affect sperm production, the authors note, most previous studies have focused on men with a history of drug abuse. Far less information is available on men who are moderate users, although studies have also found that marijuana users have higher serum testosterone concentrations.
Dr. Chavarro and his colleagues collected 1,143 semen samples from 662 men between 2000 and 2017 who were receiving treatment at a fertility clinic. The average age of the men was 36 years old, and most were white and college educated. Of this group, 317 of the participants also provided blood samples that were analyzed for reproductive hormones.
A little more than half (55%) said that they had smoked marijuana at some point, and of this group, 44% said they were past smokers and 11% classified themselves as current smokers. The men who had smoked marijuana had an average sperm concentrations of 62.7 million sperm per milliliter of ejaculate, significantly higher than men who had never smoked marijuana (45.4 million sperm per milliliter of ejaculate).
In addition, only 5% of marijuana smokers had sperm concentrations below 15 million/mL (the World Health Organization’s threshold for “normal” levels) as compared with 12% who had never smoked. The researchers did not observed any significant differences in sperm concentration between men who were current users and those who smoked in the past (59.5 vs 63.5 million/mL, respectively).
The study also found that marijuana smokers had higher levels of testosterone, the male sex hormone that plays a key role in behavior and sperm production. In fact, more intense use was associated with significantly higher concentrations of the hormone.
“Our findings were contrary to what we initially hypothesized,” said the study’s lead author, Feiby Nassan, ScD, MBBCH, MSc, a postdoctoral research fellow at Harvard T. H. Chan School of Public Health, in a statement. “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,” she added.
About the author
Roxanne Nelson is a registered nurse who has written for a wide range of publications for healthcare professionals and consumers, including Medscape, The Lancet, Prevention, Scientific American, WebMD, American Journal of Nursing, Frontline, National Geographic, Hematology Adviser, American Journal of Medical Genetics and the Washington Post, among others.