The genes we inherit may have a subtle influence over whether we experiment with and make a habit of using cannabis.
A team led by researchers from Western University in Canada, the University of California, San Diego (UC San Diego), and personal genomics and biotechnology company 23andMe compared the full genomes of 131,895 individuals with self-reported frequency of cannabis use.
In addition to identifying variations in two key genetic sequences associated with cannabis use, the study linked the same genetic patterns to more than a hundred other physical and mental health traits, providing clues on how drug use relates to our wellbeing.
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Numerous factors can affect whether an individual uses drugs for self-medication or recreational purposes, from where they live to how much money they have. Genetics often has a more indirect impact on our habits, making some prone to experimental or frequent use despite risks of ongoing harm.
"While most people who try cannabis do not go on to develop cannabis use disorder, some studies estimate that nearly 30 percent will," says Sandra Sanchez-Roige, a professor of psychiatry at UC San Diego.
"Understanding the genetics of early-stage behaviors may help clarify who is at greater risk, opening the door to prevention and intervention strategies."
The first of the genes highlighted by the researchers is Cell Adhesion Molecule 2 (CADM2), which helps handle cell assembly and nerve cell communication. It appears connected to measures of lifetime use of cannabis and frequency, based on these new findings.
Second, the gene Metabotropic Glutamate Receptor 3 (GRM3) also seems involved. It contributes to neuron signaling and long-term brain plasticity and has been linked with psychiatric disorders.
CADM2 has previously been linked to cannabis use, but not frequency, while GRM3 hasn't been connected to cannabis in prior studies. Researchers could potentially investigate how the newfound DNA variations may affect the expression/function of these genes.
The team also compared their findings to other DNA variations and gene maps, spotting overlaps with conditions including anxiety, depression, executive cognitive function, and diabetes.
"We showed that the genetics of cannabis use – both trying it and using it more often – are tied to the genetics of other psychiatric traits, cognitive measures, and even physical health problems," says Sanchez-Roige.
While the data is significant, it also suggests any potential genetic influence remains rather modest compared to other factors. Genes may explain just under 13 percent of the variation in whether individuals have tried cannabis at some point in their life, and just 6 percent of the spectrum of its frequency of use.
By pinpointing commonalities in DNA variations and how they differ between the likelihood of cannabis use and the frequency of cannabis use, it may be possible to assess risk among individuals.
"Cannabis use exists on a continuum," says neuroscientist Hayley Thorpe, from Western University in Canada.
"By studying these intermediate traits, we can begin to map how genetic risk unfolds before cannabis use disorder develops."
The research has been published in Molecular Psychiatry.