Cannabis use, both recent and long-term, has been linked to epigenetic changes in a new study. The researchers found evidence that the drug is associated with DNA methylation, a chemical alteration to the DNA inside human cells. With almost half of adults in the US having tried cannabis at least once, according to some estimates, the findings help shed more light on its potential long-term effects.
Humans have been using cannabis recreationally for thousands of years, but for much of our recent history, the practice was criminalized in many countries. That has started to change, with growing interest in the drug’s medicinal applications as well as calls for legalization in a number of hold-out regions. However, some studies have raised alarm bells by finding that, among other potential risks of long-term use, cannabis may be associated with psychiatric disorders, and that there appears to be a lack of robust evidence to back up some of the most widespread claims about its medical uses.
Against this backdrop, there’s a need to add to the scientific understanding of the effects of cannabis on the human body. A recent study aimed to find out more about what the drug could be doing to our DNA.
“Despite its growing popularity, as well as recent legalization by several states, the effect of marijuana on epigenetic factors has not been well studied,” explained senior author of the study, Dr Lifang Hou, in a statement.
Epigenetic modifications do not alter the fundamental sequence of our DNA. Instead, they are additional changes that affect how these DNA sequences are “read” by the cellular machinery. One of the best-studied mechanisms of epigenetic change is DNA methylation. Methyl groups – small molecules consisting of one carbon and three hydrogen atoms – can be tacked onto a strand of DNA, preventing neighboring genes from being expressed.
“We previously identified associations between marijuana use and the aging process as captured through DNA methylation. We wanted to further explore whether specific epigenetic factors were associated with marijuana and whether these factors are related to health outcomes,” said Hou.
The researchers analyzed blood samples from over 900 people who had previously participated in a large study called CARDIA (Coronary Artery Risk Development in Young Adults). Samples taken five years apart were assessed for each person, and they were also surveyed about their cannabis use.
The team found 22 DNA methylation markers associated with recent cannabis use, and 31 markers associated with cumulative use in the first set of samples. In the second batch of samples, 132 markers associated with recent drug use and 16 associated with cumulative use were identified.
“In our study, we observed associations between cumulative marijuana use and multiple epigenetic markers across time,” Hou summarized. “Interestingly, we consistently identified one marker that has previously been associated with tobacco use, suggesting a potential shared epigenetic regulation between tobacco and marijuana use. The observed marijuana markers were also associated with cell proliferation, infection and psychiatric disorders, however, additional studies are needed to replicate and verify these findings.”
The authors stress that it’s too soon to say whether the links between cannabis and DNA methylation, or between DNA methylation and health outcomes, are causal. The findings add to previous work that found a possible association between cannabis use and epigenetic changes, but highlight the need for more research into the long-term effects of cannabis use – something that is still lacking despite the most recent statistics finding that roughly 18 percent of Americans used the drug at least once during 2019.
“Additional studies are needed to determine whether these associations are consistently observed in different populations,” explained first author Dr Drew Nannini. “Moreover, studies examining the effect of marijuana on age-related health outcomes may provide further insight into the long-term effect of marijuana on health.”
The study is published in the journal Molecular Psychiatry.