Using cannabis may cause changes in the human body’s epigenome, a study of over 1,000 adults suggests. The epigenome functions like a set of switches, activating or deactivating genes to change how our bodies function.

“We observed associations between cumulative marijuana use and multiple epigenetic markers across time,” says Lifang Hou, a preventative medical doctor and epidemiologist from Northwestern University Feinberg School of Medicine.

Cannabis is a commonly used substance in the United States, with 49 percent of people trying it at least once, Hou and a team of US researchers report in their published paper. Some US states and other countries have made it legal, but we still don’t fully understand its effects on our health.