Heavy cannabis use has an impact on the human genome

Heavy cannabis use has an impact on human DNA but the effect is stronger in people who smoke tobacco as well.

In a new study by the University of Canterbury, scientists examined the effect of heavy cannabis use, with and without tobacco, on genome-wide DNA methylation. They found that heavy cannabis use can lead to alterations in “DNA methylation” – chemical changes in the body that influence how our genes work.

UC College of Science lecturer Dr. Amy Osborne, lead author of the UC study, said“This study shows how cannabis use is linked to changes in gene pathways that may explain the link between heavy cannabis use and those adverse health outcomes. However, in terms of the effect on the genome and DNA methylation, cannabis appears to have a distinct and somewhat more subtle effect than tobacco. It’s not altering gene pathways to the same extent, but it does affect them in particular ways.”

A total of 48 heavy cannabis users were selected from the Christchurch Health and Development longitudinal study. Scientists took their blood samples when they were aged 28 and analyzed for DNA methylation differences between cannabis users and non-users.

Scientists observed the biggest changes in those who smoked tobacco as well as cannabis. However, there there was also evidence of distinct and specific DNA alterations in those who smoked only cannabis, compared to non-users.

Most differentially methylated sites in cannabis with tobacco users were in the AHRR and F2RL3 genes. On the other hand, Cannabis-only users had no evidence of differential methylation in these genes.

Dr. Osborne, who specializes in the genomics, said, “We think assessing cannabis’s potential effect on DNA is timely. It’s currently the most widely used illicit psychoactive substance in the world, and this could be predicted to increase with decriminalization or legalization.”

Dr. Osborne says the UC study suggests that, while tobacco has a stronger effect on DNA than cannabis, cannabis appears to exert specific effects on genes involved in brain and heart function. More research with larger sample size is needed.

“Our data are suggestive of a role for DNA methylation in the biological response to cannabis. We also found the effects of cannabis use on our genomes differ from and are less pronounced than the impact of tobacco use.”

“For this reason, caution should be taken when interpreting similar cannabis exposure studies that do not, or cannot, exclude cigarette smokers.”

Journal Reference:
  1. Amy J. Osborne, Genome-wide DNA methylation analysis of heavy cannabis exposure in a New Zealand longitudinal cohort. DOI: 10.1038/s41398-020-0800-3

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