Marijuana may worsen sperm quality in men — and their sons too, study says

PULLMAN, Wash. — There’s a theory that smoking marijuana may lower a man’s sperm count. Now, new research finds marijuana may even lower the reproductive abilities of a user’s children. Scientists from Washington State University report that short-but-intense exposure to cannabis vapor lowered sperm counts and slowed sperm movement (motility) across two generations of mice. In other words, not only did the directly exposed male mice experience these changes, but their sons did as well.

This is just the latest piece of research focusing on the impact of cannabis on male reproductive function. While this project in particular focused on rodents, it does boost more controlled circumstances than most human studies, which often rely on user surveys. Moreover, this is the first study ever to expose mice to vaporized cannabis, a popular way of using marijuana among people.

While these findings aren’t definitive, study authors believe marijuana users should take note.

“This is a warning flag. You may take cannabis for some kind of momentary stress, but it could affect your offspring,” says corresponding study author Kanako Hayashi, an associate professor in WSU’s School of Molecular Biosciences, in a university release.

Regardless of marijuana use, general human sperm counts have declined by as much as 59 percent in recent decades. While it’s very unlikely marijuana is the sole reason for this trend, it may be a contributing factor for some.

Researchers studied a total of 30 adult male mice. The team exposed half of the mice to cannabis vapor three times a day for 10 days. This dosage is consistent with heavy marijuana use among humans. After that, study authors compared sperm counts and motility between the cannabis and control groups.

Interestingly, while motility declined immediately after cannabis exposure, sperm counts dropped after about a month had passed. When some of cannabis-exposed mice reproduced, their male children also showed lower than average sperm counts and motility. Furthermore, these offspring displayed evidence of DNA damage and disruptions related to sperm cell development.

“We were not expecting that the sperm would be completely gone or that motility would be completely offset, but the reduction in sperm count and motility of the offspring, the sons, is probably a direct effect of the cannabis exposure to father,” Prof. Kanako adds.

Study authors note that the cannabis-exposed rodents’ grandsons did not display any of these sperm-related abnormalities. This suggests that the cannabis impacted second-generation mice on a developmental level.

The study is published in the journal Toxicological Sciences.