Scientists warn that men attempting to conceive should avoid consuming cannabis for six months as the drug could affect sperm.
New research from Duke University has suggested that THC could impact the sperm of men in their child-bearing years and potentially the children they conceive.
Previous research has established that tobacco smoke, pesticides, flame retardants, and even obesity can alter sperm.
In the same way, the new Duke research shows that THC also affects the ways that genes are expressed and causes structural and regulatory changes in the DNA of the drug users' sperm.
Experimenting on rats and in one study with 24 men, the team found that THC targets genes in two major cellular pathways.
Their work has been published in the journal Epigenetics, although they acknowledge they haven't established whether the DNA changes triggered by THC are passed to users' children.
"What we have found is that the effects of cannabis use on males and their reproductive health are not completely null," said Professor Scott Kollins.
"There's something about cannabis use that affects the genetic profile in sperm," added Dr Kollins, a professor in psychiatry and behavioural sciences at Duke and the 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," Professor Kollins said.The study found that the higher the concentration of THC in the men's urine, the more pronounced the genetic changes to the sperm were.
"In terms of what it means for the developing child, we just don't know," said Dr Susan Murphy, the study's lead author.
She explained that it was unknown whether sperm affected by THC could be healthy enough to even fertilise an egg and continue its development into an embryo.
"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," Dr Murphy said.