Smoking Weed Might Change Your Genes

You won’t find the effects of cannabis written into your DNA, but scientists say it might be scribbling notes in the margins. A new study from Northwestern University has found that cannabis use is linked to epigenetic changes—modifications that influence how your genes are expressed without altering the DNA itself.

“We observed associations between cumulative marijuana use and multiple epigenetic markers across time,” said epidemiologist Lifang Hou, who led the research. The study followed over 1,000 adults for two decades. They reported how often they used weed, and gave blood samples at years 15 and 20.

What the researchers were looking for wasn’t damage or mutations, but changes in DNA methylation. That’s the process where chemical tags, called methyl groups, attach to DNA and dial certain genes up or down. Think of it like highlighting—or blacking out—lines in a manual. The instructions are still there, but harder to read.

Cannabis Use Linked to Changes in How Your Genes Behave, Scientists Say

Using those blood samples, the team found 31 epigenetic markers tied to cumulative cannabis use at year 15, and 16 markers at year 20. They also found dozens of markers associated with recent use—22 at year 15 and 132 at year 20. Some of these markers have been previously connected to things like immune function, hormone regulation, schizophrenia, bipolar disorder, and other substance use.

“Interestingly, we consistently identified one marker that has previously been associated with tobacco use,” said Hou, raising the possibility that marijuana and tobacco might influence the epigenome in similar ways.

To be clear, the study doesn’t say cannabis causes these changes or that it causes illness. But it does suggest cannabis leaves a biological footprint, one that might impact health over time or interact with other risk factors. All still to be seen. 

“We previously identified associations between marijuana use and the aging process as captured through DNA methylation,” said Hou. “We wanted to further explore whether specific epigenetic factors were associated with marijuana and whether these factors are related to health outcomes.”

“This research has provided novel insights,” added epidemiologist Drew Nannini, who also worked on the study. But he emphasized the need for more research—especially in different populations and across longer spans of time—to understand what these changes actually mean.

For now, it’s one more reminder that cannabis use may not be as biologically neutral as it feels. Even if it’s legal, your genes could be keeping a record anyway.