New research shows that marijuana causes genetic changes in sperm, though it’s not clear what effect those changes have, or if they’re passed on to a man’s children.
But the scientists said their findings suggest that men trying to have children should consider avoiding marijuana.
In experiments with rats and a study involving 24 men, the Duke University team found that tetrahydrocannabinol (THC) — the psychoactive ingredient in marijuana — affects genes in two major cellular pathways and alters DNA methylation, a process essential to normal development.
“What we have found is that the effects of cannabis use on males and their reproductive health are not completely null, in that there’s something about cannabis use that affects the genetic profile in sperm,” said senior study author Scott Kollins. He is a professor in psychiatry and behavioral sciences at Duke.
“We don’t yet know what that means, but the fact that more and more young males of child-bearing age have legal access to cannabis is something we should be thinking about,” Kollins said in a university news release.
For the study, the researchers compared men who were regular marijuana users (at least weekly for the previous six months) with men who had not used marijuana in the past six months and not more than 10 times in their life.
The higher the concentration of THC in the men’s urine, the more significant the genetic changes in their sperm, the investigators found.
Susan Murphy is chief of the division of reproductive sciences in obstetrics and gynecology at Duke. She said that THC appeared to affect hundreds of different genes, but many of them were associated with two of the same major cellular pathways.
One of the pathways plays a role in organs reaching their full size, while the other is involved in regulating growth during development. Both pathways can be disrupted in some cancers, she noted.
“In terms of what it means for the developing child, we just don’t know,” Murphy said.
It’s not even known if sperm affected by THC could be healthy enough to fertilize an egg and continue its development into an embryo, she added.
The findings were published online Dec. 19 in the journal Epigenetics.
The researchers plan to study larger groups of men to find out which, if any, genetic changes in THC-altered sperm are passed on to children and if those genetic changes in sperm are reversed if a man stops using marijuana.
“In the absence of a larger, definitive study, the best advice would be to assume these changes are going to be there,” Murphy said. “We don’t know whether they are going to be permanent. I would say, as a precaution, stop using cannabis for at least six months before trying to conceive.”
The U.S. National Institute on Drug Abuse has more about marijuana.