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A groundbreaking study published in Molecular Psychiatry suggests that cannabis use may lead to changes in human DNA. The study, which involved more than 1,000 adults, reveals that the human body's epigenome could be influenced by marijuana consumption. 

Researchers emphasize that they still don't fully understand the long-term health effects of these changes.

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Marijuana Use in the United States

Marijuana is the most widely used drug in the United States, according to the Centers for Disease Control and Prevention (CDC).

 In 2019, the most recent year for which data is available, approximately 48.2 million Americans, or about 18 percent of the population, reported using marijuana at least once. 

The drug has been used in the US for over a hundred years. But it is just recently become legal in some US states and other countries.

"We observed associations between cumulative marijuana use and multiple epigenetic markers across time," explained Lifang Hou, an epidemiologist from Northwestern University, when the research was published in 2023.

The Epigenomic System

The epigenome acts as a set of switches, turning genes on or off to influence how our bodies function. The study focused on these epigenetic changes, particularly DNA methylation levels, in individuals who had used cannabis recently or over an extended period.

DNA methylation is one of the most studied forms of epigenetic modification. It involves adding or removing methyl groups from DNA, which alters gene activity without changing the genomic sequence. These molecular changes make it more difficult for cells to read the genome's instructions, potentially affecting how the body functions.

Environmental and lifestyle factors, including cannabis use, can trigger these methylation changes. Importantly, these changes can be passed down to future generations. 

Blood biomarkers can provide insights into both recent and long-term exposures to such factors.

"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 “Markers” Associated with Cannabis Use

The researchers examined blood samples taken from study participants at two different points over a 20-year period. The participants, who were aged between 18 and 30 at the study's outset, provided blood samples at the 15-year and 20-year marks. 

This comprehensive data allowed the researchers to estimate cumulative cannabis use over time and compare it with DNA methylation markers in the participants' blood.

The study identified numerous DNA methylation markers associated with cannabis use. In the 15-year blood samples, researchers found 22 markers linked to recent cannabis use and 31 markers associated with cumulative use. By the 20-year point, they had identified 132 markers related to recent use and 16 linked to cumulative use.

"Interestingly, we consistently identified one marker that has previously been associated with tobacco use," Hou noted, "suggesting a potential shared epigenetic regulation between tobacco and marijuana use."

Implications and Future Research

Several of the epigenetic changes associated with cannabis use have previously been linked to conditions such as cellular proliferation, hormone signaling, infections, and neurological disorders like schizophrenia and bipolar disorder, as well as substance use disorders.

 However, it's important to note that this study does not prove that cannabis directly causes these changes or related health problems.

"This research has provided novel insights into the association between marijuana use and epigenetic factors," said Drew Nannini, an epidemiologist from 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."