Does Marijuana Use Affect Sperm?

My partner and I are having a debate. He’s a semi-regular weed smoker and I don’t usually have a problem with that. However, we’ve been trying for our first baby, and I can’t help but wonder if his marijuana use has an effect on his sperm or ability to have kids. Any information on pot and sperm counts?
—Anonymous

There is continual speculation that marijuana consumption could lower sperm counts or, more generally, impact sperm. It’s not just the number of sperm you have that is relevant. It’s the quality — their shape (morphology), how good they are at swimming (motility), etc. There are lots of things that affect sperm. Tight underwear, for example.

In mice, marijuana exposure is linked to infertility. There are biological reasons to think the link might be in people too. There is a 2021 review that pulls together what we know about marijuana consumption and sperm parameters. It does conclude that marijuana is linked to lower sperm counts and worse sperm quality.

However, the evidence is limited. Part of the problem is that sperm quality evaluation isn’t something that people typically do for fun; it usually happens as a result of an evaluation for subfertility or infertility.

A 2025 study gets around some of these problems, albeit with a small sample size. This study uses 113 men, including both tobacco smokers and cannabis users, along with some men who do not use either. It found that normal sperm morphology was decreased in both tobacco and cannabis users. Sperm motility was also affected, although there were no differences in sperm concentration.

An even better study design would exploit the fact that sperm gets regenerated over time. One could take a cohort of marijuana users and randomly have half of them abstain for a certain period and measure their sperm. I don’t know of anyone who has done this, but I hope that someone does. For now, the data seems strongly suggestive. If you are trying to conceive — and especially if you’re struggling — it is worth considering whether a change in cannabis use might help.