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Does Marijuana Make Your Sperm “Abnormal”?


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Well, here are some findings about the relationship between the shape of a dude’s sperm and how much weed he smokes (since you asked).

It’s a common belief, apparently, that drinking booze and smoking cigarettes can make men less fertile (or being obese, or wearing tight underwear). But according to a new study, these activities actually don’t impact sperm at all. Marijuana, on the other hand, was the only substance in the study found to have a considerable impact—in fact, it could double the chances of a guy under 30 producing abnormal sperm, hiking his risk of infertility.

In the largest study of its kind, researchers in England examined the impact of certain lifestyle habits—like drinking and smoking—on men’s sperm size and shape (known as “sperm morphology”). Sperm with abnormal morphology are thought to be weaker swimmers, making it harder for them to fertilize an egg.

Cross-analyzing the sperm samples with the men’s lifestyle habits and other factors, the researchers found only two strong correlations: Guys with abnormal sperm samples were nearly twice as likely to have ejaculated during the summer, or to have smoked weed in the three months prior to ejaculating. These findings should be taken with a grain of salt, however, since correlation does not imply causation and other unknown factors could have played a part.

“Our knowledge of factors that influence sperm size and shape is very limited, yet faced with a diagnosis of poor sperm morphology, many men are concerned to try to identify any factors in their lifestyle that could be causing this,” says study lead Dr. Allan Pacey, a specialist in male fertility at Sheffield University.

The study didn’t examine why pot might impact sperm shape. But Dr. Pacey suggested that for couples who are trying to have a baby, “the sensible thing to do” is for the guy to lay off the weed for up to three months—which is how long it takes to make sperm.

Still, weed or no weed, the number one predictor of normal sperm morphology and male fertility is ultimately genetics. And if there’s one sure thing to be gleaned from this study, it’s that men’s habits actually have less impact on their sperm than was previously believed. “There are fewer risks than people think, and that makes sense to me,” says Pacey. “The single thing that affects fertility is how big your testicles are. If you’re blessed with big testicles, you’ll produce more sperm.” So, there you go.