Researchers have announced that tetrahydrocannabinol (THC), an active ingredient in marijuana, affects epigenetics, triggering structural and regulatory changes in the DNA of users’ sperm. It is so far unknown whether these changes are passed on to children, and what effects they could have.

Rat models and a study of 24 men found that regular THC use seems to target hundreds of genes in two cellular pathways and alters DNA methylation, which ensures normal development. One of these cellular pathways is involved in helping organs reach their full size, while the other regulates growth during development.

Regular users were defined by the study as those who smoked marijuana at least once a week for the last six months. The higher the concentration of THC in urine, the more evident it was that that person’s sperm had undergone genetic changes.

The study was limited by the amount of men who took part. The findings could also be influenced by other factors such as sleep, alcohol use and other lifestyle habits.

The next step in this research, the scientists said, was to conduct larger studies and determine whether changes in sperm are reversed when marijuana usage declines. They are also intending to test umbilical cord blood of babies born from THC-altered sperm to find any epigenetic changes which have taken place.