Cannabis use has become much more common in the United States as many states have legalized it for medical or recreational use.
In 2019, about 48.2 million Americans, or roughly 18% of the population, reported using cannabis, according to the U.S. Centers for Disease Control and Prevention.
Cannabis, also called marijuana, comes from the Cannabis sativa plant. People may smoke it, use it in water pipes, eat it in foods or take it in other forms, but scientists are still working to understand what regular or long-term use may do inside the body.
A study led by researchers at Northwestern Medicine found that cannabis use was linked to changes in chemical marks on DNA. The research was published in the journal Molecular Psychiatry.
DNA carries the biological instructions that help cells function, grow and repair themselves. The basic DNA code does not have to change for the way genes work to change, because the body can add small chemical marks that affect whether certain genes become more or less active.
One of these processes is called DNA methylation. It involves chemical tags attaching to DNA, and researchers often study these tags because they may reflect the effects of aging, lifestyle and environmental exposures.
The Northwestern team wanted to know whether cannabis use was associated with this type of change. The researchers examined blood samples and health information from more than 900 adults who had taken part in a long-running study of heart health.
Participants had provided blood samples at two different times, about five years apart. They also reported their recent cannabis use and gave researchers information that could be used to estimate how much cannabis they had used over their lifetime.
The scientists then examined DNA from the blood samples. They found dozens of sites where DNA methylation patterns were associated with cannabis use, with the number of identified markers ranging from 16 to 132 depending on the measure and time point studied.
Some of the affected areas were connected with biological processes involving cell growth, hormone activity and the immune system. Other signals appeared in areas previously associated with conditions such as schizophrenia, bipolar disorder and substance use disorders.
That does not mean cannabis causes these conditions. It also does not mean that people who use cannabis will develop a particular disease simply because researchers found changes in DNA methylation.
The study showed an association rather than direct cause and effect. Other factors in a person’s life, including tobacco use, alcohol use, diet, stress, environmental exposures and underlying health differences, can also influence chemical marks on DNA.
Researchers therefore need more studies to understand what the observed changes actually mean. An important question is whether they disappear after a person stops using cannabis or whether some remain for years.
Scientists also want to know whether these DNA changes have meaningful effects on health. Future research could examine whether they are connected with later risks of heart disease, mental health problems or other conditions, and whether the effects differ according to how often or how much cannabis is used.
The findings are especially relevant as cannabis products become easier to obtain and public attitudes toward the drug change. Legal availability does not necessarily mean that every form of cannabis use is harmless, just as finding a biological change does not automatically mean that the change is dangerous.
Cannabis is already used medically in some situations, and research continues into both its possible benefits and its risks. Its effects can also vary depending on dose, frequency of use, age, health, the type of cannabis product and other substances a person uses.
The study adds another piece to a complicated picture. By examining changes at the DNA level, researchers may eventually gain a better understanding of how cannabis affects the body over time and which people may be more vulnerable to unwanted effects.
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