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Is Smoking Weed Really Bad for Sperm? Here’s What the Science Says

A new study adds to a growing body of evidence that marijuana seriously impacts sperm health. Here’s what would-be dads need to know.

Leaf shape via freepik; illustration by Anne Meadows

Men who want to become dads and occasionally smoke weed are often paranoid about their sperm — and not just because they’re stoned. It’s natural to ask “Is smoking weed, um, bad for my boys?” While a growing body of research links excessive marijuana use to male infertility, a new study suggests that there may be other risks: When these men are able to conceive, in spite of smoking weed, it could increase their child’s risk of autism. While the findings raise many important questions for couples trying to become parents, they raise even more questions for doctors and scientists trying to understand marijuana’s effects on sperm and determine whether smoking pot while trying to conceive can be considered safe, even in small amounts. 

Prior to the current research, questions of sperm and marijuana were mostly related to fertility. Doctors advise against cannabis for men trying to conceive based on studies that show what it does to sperm — heavy use lowers sperm counts, decreases sperm motility (basically, their ability to swim), and increases sperm malformation. But obviously that does not mean that weed inevitably renders sperm useless. If it did, teens would use it as a contraceptive and Phish fans would have gone extinct.

But the medical and scientific consensus is that if a couple is having trouble getting pregnant, then it’s not a good idea for the guy to smoke pot. “All we can say is that your swimmers may not be as healthy as they could be if you did not have marijuana in your system,” says Dr. Jamin Brahmbhatt, a urologist and sexual health expert at Orlando Health. “For my male infertility patients, I do recommend stopping marijuana to maximize fertility.” 

And for men who are not particularly worried about fertility issues, marijuana in small doses can help combat erectile dysfunction and boost female libido, making it easier to have sex and therefore, theoretically, easier to conceive. Unless they’re struggling with infertility, most pot-smoking couples net out somewhere in the middle, dabbling without overdoing it. Plenty of men can smoke pot and still get someone pregnant. 

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The more important question is, what happens when they do?

If this new study is any indication, weed may have more of an impact than previously thought. “We were surprised to find this significant association between marijuana use in men and changes in this gene that is implicated in autism,” says study coauthor Rose Schrott, a Ph.D. student at Duke UniversityAfter conducting another study that demonstrated 177 potential genetic changes in the sperm of men who use marijuana, Schrott decided to zero in on those specific genes. Using 24 men, 12 users and 12 non-users, animal models, and a genome-wide analysis of the activity of segments of DNA, they found that when men smoked or ingested marijuana, the Discs-Large Associated Protein 2, or the DLGAP2 gene, underwent notable methylation. This matters because DLGAP2 gene identified is strongly associated with autism as well as schizophrenia and post-traumatic stress disorder.

“Our initial study was really the first of its kind to look at marijuana use in men and changes to his sperm, so we didn’t necessarily expect to see this gene being implicated, but it was a finding that we felt warranted follow-up given its potential involvement in autism and schizophrenia,” Schrott says. 

Since it is the first study of this kind, the findings are very much prospective and need to be duplicated with a larger sample size before there is any reason for men to panic. “We are only able to report this association present in the sperm of men who use marijuana. So what this means for children, we don’t know,” Schrott adds.

Dr. Jordan Tishler, a physician and Harvard-trained Holistic Care expert, believes that if the risks of smoking weed were that significant, we’d see the effects more prominently in society. That is not to say that cannabis use while trying to conceive is risk-free, but those smaller risks need to be carefully examined through many more formal studies. 

“There is no evidence that heavy users have trouble conceiving or have an increased risk of ill children. However, no studies looking for those outcomes have been done to date,” he notes. 

It is tempting to jump to the conclusion that the rise in autism cases could be attributed to the mainstreaming of marijuana, as the domestic production of it has increased tenfold over the past 25 years. Still, it is important to stress that the current study does not directly link men’s marijuana use to autism in their offspring, but rather calls for much more research on the matter. Until then, the largest risk prospective dads run with weed is guilt if something does go wrong during the pregnancy. There may be no way to be certain that cannabis caused the problem, but if parents are going to feel terrible about that for the rest of their child’s life, then they should probably take a break from the weed. 

“If the man or the couple are worried about cannabis use during conception and are likely to feel that they did something wrong if they have a damaged child,” Tishler says, “then cannabis should be avoided.” When it comes to conception, it’s not exactly worth the risk.