Researchers Link Regular Cannabis Use to Male Infertility, While Others Say “Not So Fast”

Updated 10/18/2021

The Dude might abide, but could the iconic stoner make a baby? According to a 2019 study from Duke, smoking all that ganja not only might have impaired the fertility of The Big Lebowski’s cannabis-loving character due to a lowered sperm count, but it also could have affected his sperm’s genetic makeup. No amount of munchies could fix that. Interestingly, another respected study from Harvard says just the opposite—so what’s happening in the science world? It’s academia vs. academia, or perhaps a case of reefer madness! Let’s look at the conclusions each study makes.

The case for lower sperm count: the Duke study

Scientists are just beginning to connect the dots between regular marijuana use and its negative health implications, and a  2019 published study by the Duke University Medical Centre in Durham, NC has found that the illicit drug affects sperm production and DNA.

But as legalization of cannabis spreads across the country, researchers are concerned about the number of men who could be affected by this potential fertility threat. Of course, The Dude is no spring chicken—and probably well past his baby-making years—but there’s a whole generation of younger men living in the dawn of cannabis legalization who might be affected by its health consequences.

“What we have found is that the effects of cannabis use on males and their reproductive health are not completely null, in that there’s something about cannabis use that affects the genetic profile in sperm,” said Scott Kollins in Duke Health News and Media, one of the authors of the study. “We don’t yet know what that means, but the fact that more and more young males of child-bearing age have legal access to cannabis is something we should be thinking about.”

Regular cannabis use lowers your chances of getting pregnant

According to the World Health Organization, marijuana is the most widely-consumed drug on the planet, used by about 147 million people each year—or around 2 percent of the world’s population. As legal access spreads across the U.S. (right now, it’s legal in 10 states and decriminalized in another 13), scientists are beginning to look at the effects of its active ingredient, tetrahydrocannabinol (THC), in teens, adults and pregnant women.

The new research suggests that men of childbearing age should be more cognizant of the effects of smoking weed—and the exposure to THC in particular—just the way they would for alcohol or tobacco use. The Duke Health study was small, only 24 men participated (and a whole bunch of rats), but it connected for the first time high amounts of THC in urine to a lowered sperm count. On average, the sperm concentration in the semen of the 12 non-smokers in the study was about twice as high as it was in the 12 smokers, the study revealed. In other words, that big spliff could someday get in the way of your ability to make a baby.

If you enjoy cannabis regularly— which experts define as smoking weed at least once a week over the course of six months — and are worried about whether it’s affected your sperm count, you should consider having that tested. SpermCheck is an over-the-counter kit that can help you determine your fertility status discretely and accurately right at home.

Marijuana can affect the genetic profile in sperm

The bigger implications of regular cannabis exposure uncovered in the study is that pot smokers had changes in their sperm genetic profile that, in other studies, have been associated with abnormal growth and cancer. What’s unclear is whether these changes in sperm quantity and quality could affect the fertilization process and the health of the offspring, but the researchers advise caution nonetheless.

“In the absence of a larger, definitive study, the best advice would be to assume these changes are going to be there [in sperm],” said lead author Susan Murphy, the chief of the Division of Reproductive Sciences in the Department of Obstetrics and Gynecology at Duke University Medical Center in North Carolina. “I would say, as a precaution, stop using cannabis for at least six months before trying to conceive.”

The good news is that the changes is sperm quantity and quality might not be permanent, Murphy told Live Science, as men generate new sperm daily. It takes around 70 days for sperm to mature and if not ejaculated, they’re absorbed into the body. What’s unknown is whether sperm damaged by pot smoking could negatively affect offspring. But, Murphy pointed out, “assuming that said sperm is viable, capable of fertilization and results in a viable embryo,

in terms of what it means for the developing child, we just don’t know.” It’s unknown whether sperm affected by THC could be healthy enough to even fertilize an egg and continue its development into an embryo, she said.

The case for higher sperm count: the Harvard study

The Harvard study’s summary states: “Men who had ever smoked marijuana had higher sperm concentration and count and lower serum FSH concentrations than men who had never smoked marijuana; no differences were observed between current and past marijuana smokers.”

The number of human participants in this study was much larger than Duke’s (with fewer rats too, perhaps): 662 men participated and 1,143 semen samples were collected. The 365 men in the study who said that have smoked pot at some point in time had significantly-higher sperm concentration (63 million sperm/ml vs. the average 45 million/ml) than those who have never had a single hit..

Lead researcher Jorge Chavarro cautions that, despite the higher sperm-count for weed aficionados, these findings do not necessarily mean that smoking pot can lead to greater chances of successful conception for the man’s partner. He also admits that the results of the surprising (certainly in light of other studies finding the exact opposite, this is something of an understatement): “These unexpected findings…highlight that we know too little about the reproductive health effects of cannabis…We know a lot less than we think we know.”

So what about YOUR fertility, dude?

In light of these seemingly conflicting studies, what are guys to do? If you’re worried about whether cannabis has affected your fertility, it’s not a bad idea to test your sperm count with SpermCheck and reduce your exposure while you are actively trying to get pregnant. Even The Dude might agree that moderation is something everyone can abide when trying to conceive.