Cannabis use has become increasingly common in the United States as more states have legalized it for medical or recreational purposes.
But scientists are still working to understand what regular or long-term cannabis use may do inside the body.
A study from Northwestern Medicine offers one clue. Researchers found that cannabis use was associated with changes in chemical marks on DNA, although the study did not prove that cannabis directly caused those changes.
DNA contains the biological instructions that help cells function. Most cells carry essentially the same genetic code, but they do not use every gene in the same way or at the same time.
One way the body controls gene activity is through a process called DNA methylation. Small chemical tags can attach to DNA and influence whether certain genes become more or less active without changing the underlying genetic code itself.
These chemical patterns can be affected by many things, including aging, environment, diet, disease and exposure to substances such as tobacco. Researchers wanted to know whether cannabis use might also be connected with measurable changes in these patterns.
The Northwestern Medicine team analyzed blood samples from more than 900 adults who were participating in a long-running study of heart and blood vessel health. The participants had provided blood samples at two different times, about five years apart.
They also reported information about their cannabis use. Researchers considered both recent use and estimated cumulative use over the participants’ lifetimes.
The scientists then examined DNA from the blood samples for methylation patterns associated with cannabis exposure. They found dozens of sites where these chemical marks differed in connection with reported cannabis use.
Depending on the measure and time point examined, the researchers identified between 16 and 132 DNA markers associated with cannabis use. Some were found near genes involved in processes such as cell growth, immune activity and hormone regulation.
Several of the identified areas had also been connected in previous research with psychiatric or substance-related conditions. These included schizophrenia, bipolar disorder and substance use disorders.
However, this does not mean cannabis use causes these conditions through DNA changes. A shared DNA marker can be connected with several biological processes, and an association alone cannot show which factor came first or whether another factor explains the relationship.
There are also many possible influences that are difficult to separate completely in this kind of research. People who use cannabis may differ from non-users in tobacco or alcohol use, medications, diet, stress, environmental exposures and other health-related behaviors.
Another important point is that the researchers examined DNA methylation in blood. Chemical changes found in blood cells do not necessarily tell scientists exactly what is happening in the brain, lungs or other organs affected by cannabis.
Even so, the findings are useful because they identify specific biological signals that future researchers can investigate. Scientists can now ask whether the same patterns appear in other populations and whether they change when cannabis use increases, decreases or stops.
Researchers may also investigate whether different forms of cannabis have different effects. Smoking, vaping and eating cannabis can expose the body to different chemicals and produce very different amounts and patterns of THC, the main substance responsible for cannabis’s intoxicating effects.
The strength of modern cannabis products also varies widely. This makes it difficult to treat all cannabis exposure as if it were the same, particularly when trying to understand possible long-term health effects.
Lead investigator Dr. Lifang Hou and colleagues said more research is needed to determine whether the DNA changes have meaningful consequences for health. Long-term studies could examine whether these biological patterns are connected with later heart disease, mental health problems or other conditions.
The research was published in Molecular Psychiatry. It adds to a growing body of work examining cannabis not only through its immediate effects on mood and behavior, but also through subtle biological changes that may occur over time.
The study’s biggest limitation is that it cannot establish cause and effect. Self-reported cannabis use may also be imperfect, and DNA methylation is influenced by many factors that can make it difficult to identify the effect of a single exposure.
For now, the findings should not be interpreted as proof that cannabis permanently damages DNA. Instead, they show that cannabis use is associated with measurable differences in how DNA may be regulated, giving scientists another avenue for studying the drug’s possible long-term effects.
As cannabis becomes more widely available, this kind of research will become increasingly important. Better evidence about dose, frequency, method of use and long-term biological effects can help people make more informed decisions about a substance whose health effects are still not fully understood.
Copyright © 2026 Knowridge Science Report. All rights reserved.
