Cannabis use could leave enduring traces in the human body, according to a 2023 study involving more than 1,000 adults. The effects would not alter the DNA sequence itself, but could influence the way that genetic code is expressed.
US scientists reported that cannabis may affect the epigenome, a system of molecular switches that turns genes involved in bodily functions on or off. A systematic literature review published in 2024 by Portuguese researchers supported these findings.
"We observed associations between cumulative marijuana use and multiple epigenetic markers across time," epidemiologist Lifang Hou of Northwestern University said in 2023.
Cannabis use and epigenetic changes
In their published paper, Hou and her colleagues noted that cannabis is widely used in the US, where almost half of Americans have tried it at least once.
Although some US states and other nations have legalised cannabis use, its health effects are still not completely understood.
To explore the issue, the team examined information from a long-term health study that followed roughly 1,000 adults for two decades.
The participants were aged between 18 and 30 when the study started. Over the years, they completed surveys about their cannabis use and provided blood samples after 15 and 20 years.
Using blood samples collected five years apart, Hou and her colleagues assessed epigenetic changes-particularly DNA methylation levels-in people who had used cannabis recently or over a prolonged period.
The attachment or removal of methyl groups from DNA is among the most extensively researched epigenetic alterations.
Without modifying the genomic sequence, DNA methylation can affect how readily cells ‘read’ and interpret genes, rather like obscuring important lines in a set of instructions.
Environmental and lifestyle influences can bring about these methylation changes. They may be inherited by future generations, while blood biomarkers can reveal both recent and past exposures.
"We previously identified associations between marijuana use and the aging process as captured through DNA methylation," Hou said.
"We wanted to further explore whether specific epigenetic factors were associated with marijuana and whether these factors are related to health outcomes."
DNA methylation markers linked to cannabis use
The detailed records of participants’ cannabis use enabled the researchers to calculate both cumulative use over time and recent use, then compare these measures with DNA methylation markers in the blood.
In blood samples taken at year 15, they identified numerous DNA methylation markers: 22 associated with recent use and 31 associated with cumulative cannabis use.
Among the samples collected at the 20-year stage, the researchers found 132 markers connected with recent use and 16 connected with cumulative use.
"Interestingly, we consistently identified one marker that has previously been associated with tobacco use," Hou explained, "suggesting a potential shared epigenetic regulation between tobacco and marijuana use."
Several epigenetic alterations associated with cannabis use had previously been connected with cellular proliferation, hormone signalling, infections, neurological conditions such as schizophrenia and bipolar disorder, and substance use disorders.
What the study does not establish
Importantly, the research does not demonstrate that cannabis directly causes these changes or that it leads to health problems.
"This research has provided novel insights into the association between marijuana use and epigenetic factors," said epidemiologist Drew Nannini of Northwestern University.
"Additional studies are needed to determine whether these associations are consistently observed in different populations. 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 was published in Molecular Psychiatry.
An earlier version of this article was published in July 2023.
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