Cannabis Impacts Sperm Quality – And Possibly Future Generation's Too, Mouse Study Suggests

We all know about the dangers of secondhand smoke, but here’s a slant we bet you weren’t expecting: inhaling cannabis vapor might affect sperm quality – in your offspring.

A new study, published in the journal Toxicological Sciences, has found that mice who experienced an intense but short exposure to cannabis vapor had reduced sperm counts and slower sperm movement. So far, so well-established – but what’s surprising is that the same effect was seen in the offspring of these stoner mice. Not only did their sons have lowered sperm motility and count, but they also showed evidence of DNA damage and disrupted sperm development.

“This is a warning flag,” said study co-author Kanako Hayashi. “You may take cannabis for some kind of momentary stress, but it could affect your offspring.”

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Cannabis is already well known to be associated with reduced sperm count and motility, as well as what the scientists euphemistically term “abnormal morphology” – that is, it makes your sperms look weird. The evidence from the new study supports that: the researchers took 30 adult male mice and split them into two groups, one of which they put on a strict high-cannabis diet.

Three times a day, for ten days, the mice were exposed to vaporized whole cannabis – previous studies of this nature have generally used methods like THC injections, but it’s not exactly the method most humans use to get high, so the researchers went a different route. When the team compared the sperm counts and motility between the stoner mice and the straight-edge mice, they found some clear differences: among the test group, sperm motility was lower immediately following exposure. In fact, sperm counts were lower even a whole month after the experiment.

But that wasn’t all. When the researchers bred several of the test mice with females that had never used weed, they made a surprising discovery. Male babies were born with signs of DNA damage in their testes, including increased levels of a gene associated with various developmental disorders. Despite not being exposed directly to cannabis, they too had reduced sperm quality.

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

Once the researchers reached a third generation of mice, however – the grandsons of the original party rodents – the impacts of the cannabis exposure were gone. This hints at the mechanism behind the reduction in sperm quality over the first generation, the researchers suggest: the cannabis exposure must affect the mice at a very early developmental stage, they think.

In fact, that’s what they’re testing now: the team theorize that cannabis exposure in utero might have even deeper generational effects. While the experiments may only be in mice so far, the message is clear: if you’re hoping to make a baby in the near future, you’d better lay off the reefer.

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