There has been considerable debate about the safety of marijuana, which has only increased since the drug has been legalized in a number of states for both medicinal and recreational purposes. Scientists are finally beginning to be able to research the impacts of the drug, an effort that was stymied for decades by the classification of marijuana as a dangerous drug.
New research from scientists at Duke University has suggested that one of the psychoactive compounds in marijuana, tetrahydrocannabinol (THC) has an impact on men’s sperm. Like other environmental factors such as pesticides, flame retardants, tobacco smoke, and obesity, THC appears to affect the epigenetics of sperm. Epigenetics can have a significant impact on the structure and regulation of DNA, influencing how and when genes are expressed. The peer-review study has been reported in the journal Epigenetics, which is an open-access journal.
In this work, the researchers assessed both a rodent model and human users of THC. Their work showed that THC can target genes that are a part of two cellular pathways and change DNA methylation, one of the most common epigenetic tags that's added to DNA. Methylation is also critical to the normal development of an organism.
"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 the senior author of the work, Scott Kollins, Ph.D., 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 added.
This study compared people who were regular users, meaning they smoked marijuana at least once a week for the previous six months, with people who had not smoked the drug in at least six months and had not used more than ten times in their entire lives. The research did reveal that as THC levels in urine increased, more genetic changes were seen in sperm.
There is still a lot the researchers don’t know, however. While some studies have suggested that epigenetics are passed on to children from their father through the sperm, it’s not known whether THC triggers changes that are inherited. This study also had a small sample size; 24 men completed the study, a dozen were in the user group and the other dozen in the non-user group.
The genes that were impacted by THC in humans and rats were different, the researchers noted. But, the same two cellular pathways ended up being affected, said the lead author of the work, Susan K. Murphy, Ph.D., an associate professor and chief of the Division of Reproductive Sciences in obstetrics and gynecology at Duke.
One pathway helps regulate the size of organs; the other is an important part of growth regulation during development. Both of the pathways have been found to be disrupted in some forms of cancer.
"In terms of what it means for the developing child, we just don't know," Murphy said. It remains to be seen whether sperm that’s been altered by THC is healthy enough to fertilize an egg and move forward with embryonic development, she noted.
This work is a starting point, and the scientists plan to continue their study. They want to expand the sample size and learn more about the participants’ habits as well. They also want to know how those epigenetic changes are impacting children.
As the legalization of marijuana expands nationally, and the public becomes more accepting of use, it will be important to ensure that we know what marijuana is doing to the body.
"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, 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."