Cannabis use has become increasingly common in the United States as more states allow it for medical or recreational purposes.
Millions of Americans now report using cannabis, but scientists are still working to understand what regular or long-term use may do inside the body.
Cannabis comes from plants in the Cannabis genus and can be used in several ways. People may smoke it, inhale it through other devices, eat it in foods or consume it in drinks and other products.
Much of cannabis research has focused on its effects on the brain, mood, memory and heart. A study from Northwestern Medicine took a different approach by examining whether cannabis use is associated with chemical changes that can affect how genes behave.
The researchers studied a process known as DNA methylation. This does not change the basic genetic code itself, but it involves small chemical tags attaching to DNA and can influence whether certain genes become more or less active.
These changes are part of what scientists call epigenetics. Epigenetic changes can be influenced by many things, including aging, diet, smoking, environmental exposures and other aspects of a person’s life.
The study was led by Dr. Lifang Hou of Northwestern University and was published in the journal Molecular Psychiatry. Researchers examined blood samples and health information from more than 900 adults who had participated in a long-running study of cardiovascular health.
Participants had provided blood samples at two examinations about five years apart. They also reported their cannabis use, allowing researchers to look at both recent use and estimated use over a longer period.
When the scientists examined DNA from the blood samples, they found numerous sites where methylation patterns were associated with cannabis use. Depending on the time point and measure of cannabis exposure, the researchers identified dozens of these DNA markers.
Some of the affected areas were connected with biological processes involved in cell growth, immune function and hormone activity. Other signals were found near genes previously associated with neurological or psychiatric conditions and substance use.
One particularly interesting finding involved a marker previously associated with tobacco use. Because some cannabis users also smoke cigarettes, the researchers considered cigarette smoking and other factors when analyzing the results.
However, the findings do not show that cannabis directly caused the DNA changes. An observational study can identify an association, but it cannot prove that one factor is responsible for another.
It is also unclear whether the DNA differences found in the study cause any disease or other health problem. Some biological changes may have little effect, while others could potentially influence health over time.
That uncertainty makes further research important. Scientists need to determine whether the same patterns appear in other populations, whether they change when people stop using cannabis and whether the amount or frequency of cannabis use makes a difference.
Researchers also want to understand whether these DNA changes could eventually help explain links between cannabis use and certain health conditions. Larger and longer studies could examine whether particular methylation patterns are associated with later changes in cardiovascular, mental or general health.
The findings are especially relevant as cannabis products become easier to obtain and often contain different amounts of THC, the main chemical responsible for the drug’s intoxicating effects. Today’s cannabis market also includes a wide variety of products, making it difficult to treat all cannabis exposure as the same.
The Northwestern Medicine research adds another piece to a complicated scientific picture. Cannabis may have medical uses for some conditions, but widespread availability does not mean researchers fully understand all of its long-term effects.
For people deciding whether to use cannabis, the study does not provide a simple answer about whether it is harmful or safe. Instead, it shows that cannabis use is associated with measurable biological differences and that scientists still need to determine what those differences mean for long-term health.
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