As legal access to cannabis expanding, more scientists are studying the effects of its active ingredient, tetrahydrocannabinol (THC), in teens, adults and pregnant women.
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Previous research has shown that tobacco smoke, flame retardants, pesticides, and even obesity can alter sperm. Duke research shows THC also affects epigenetics, triggering structural and regulatory changes in the DNA of users’ sperm.
The researchers study the impact of the THC in rats and with 24 regular male users. The study defined regular users as those who smoked cannabis at least weekly for the previous six months. Their sperm were compared to those who had not used cannabis in the past six months and not more than 10 times in their lifetimes.
According to the study, the higher the concentration of THC in the men’s urine, the more noticeable the genetic changes to their sperm were.
The researchers found that THC appears to target genes in two major cellular pathways. It alters the DNA process essential to normal development. One of the pathways is involved in helping bodily organs reach their full size; the other involves a large number of genes that regulate growth during development. Both pathways can become dysregulated in some cancers.
The team does not yet know whether DNA changes activated by THC are passed to men’s children and what effects that could have. Their findings published in the journal Epigenetics.
Scott Kollins, Ph.D., professor in psychiatry and behavioral sciences at Duke and senior author of the study said: “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
“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 terms of what it means for the developing child, we just don’t know,” said lead author Susan K. Murphy, Ph.D. “It’s unknown whether sperm affected by THC could be healthy enough to even fertilize an egg and continue its development into an embryo, she said.
The study was a starting point on the epigenetic effects of THC on sperm and is limited by the relatively small number of men involved in the trial, Murphy said. The findings in men also could be confounded by other factors affecting their health, such as their nutrition, sleep, alcohol use and other lifestyle habits.
The Duke team plans to continue its research with larger groups. They intend to study whether changes in sperm are reversed when men stop using marijuana. They also hope to test the umbilical cord blood of babies born to fathers with THC-altered sperm to determine what, if any epigenetic changes, are carried forward to the child.
“We know that there are effects of cannabis use on the regulatory mechanisms in sperm DNA, but we don’t know whether they can be transmitted to the next generation,” Murphy said.
“In the absence of a larger, definitive study,” Murphy said. “The best advice would be to assume these changes are going to be there. 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.”