The advice stems from new research into the possible effects of cannabis' active ingredient tetrahydrocannabinol (THC) on sperm.

By Maressa Brown

December 20, 2018

As more and more states are passing progressive laws around cannabis use, science is stepping up to the plate to give users more information about its active ingredient tetrahydrocannabinol (THC). Researchers are investigating all different angles of its effects on teens, adults, pregnant women, and now, men who are trying to conceive. Based on a new study out of Duke Health, published in the journal Epigenetics, experts say men would do well to want to refrain from cannabis use for six months before trying for a baby.

A release from Duke University Medical Center notes that much like previous research around tobacco, pesticides, flame retardants, and even obesity, THC can certainly affect epigenetics—the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself—according to their findings. In this case, that means that cannabis use could create structural and regulatory changes in the DNA of users' sperm.

The Duke research was conducted on both rats and in a very small study of 24 men. In the human study, men who were defined as regular cannabis users smoked cannabis at least weekly during the previous six months. The researchers then compared their sperm to that of men who hadn't used cannabis in the past six months and not more than 10 times over the course of their lives. They noticed that the higher the concentration of THC in a man's urine, the more pronounced their sperm's genetic changes were.

Ultimately, they observed that THC appears to target genes in two major cellular pathways and alters DNA methylation, a process essential to normal development. The release explains that one of the pathways is involved in helping bodily organs reach their full size, while the other involves a large number of genes that regulate growth during development. Both pathways can become dysregulated in some cancers.

That said, researchers don't know what these DNA changes mean for babies, noting that it's unclear whether they'll be passed down to the next generation or lead to a particular downstream effect.

"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 Scott Kollins, Ph.D., professor in psychiatry and behavioral sciences at Duke and senior author of the study. "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."

The authors also note that this research is just a jumping off point on the epigenetic effects of THC on sperm, and it was limited, given the number of men involved and the fact that it was not controlled for other factors like nutrition, sleep, alcohol use, and other lifestyle habits.

The next step will be to do similar research with larger groups and to see if curbing cannabis use will reverse changes in sperm. Another cool, next-level approach: testing the umbilical cord blood of babies born to dads with THC-altered sperm to determine what, if any epigenetic changes, might be passed down to a little one.

In the meantime, lead author Susan K. Murphy, Ph.D., associate professor and chief of the Division of Reproductive Sciences in obstetrics and gynecology at Duke, offered the following words of wisdom to cannabis users looking to become parents: "In the absence of a larger, definitive study, 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."

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