This Gene May Increase Your Chances of Developing a Cannabis Addiction

Certain cannabis users have a higher chance of developing an addiction than others, and, according to new research, it may be down to their genes. 

In a new study published by Nature, scientists in Denmark claim for the first time to have found a genetic marker for cannabis use disorder (CUD), an addiction to marijuana thought to affect around 1.5 percent of Europeans and Americans. 

As with other forms of addiction, CUD is typified by cravings and withdrawal symptoms when cannabis isn’t taken. And fittingly, the genetic marker the Danish researchers found for CUD also regulates the levels of a brain receptor that binds to nicotine. 

But to ensure that this addiction association wasn’t just a genetic coincidence, the team had to check thousands of individual genomes. 

“We had a Danish cohort of around 2,300 individuals with cannabis use disorder. And then we have around these 48,000 individuals in the control group,” said Ditte Demontis, an associate professor at Aarhus University in Denmark, who led the work. 

By comparing thousands of genomes from people with CUD to those who didn’t display it, Demontis and her team identified a single variant of the gene CHRNA2. And to further ratify their findings, the researchers expanded their study to screen a database of Icelandic genomes, which included 5,500 people with CUD and 300,000 without. 

“So after screening the whole genomes, we have been able to identify one genetic variant that can be associated with cannabis use disorder. And even more importantly, we have actually been able to replicate this finding in an independent cohort from Iceland,” Demontis told Analytical Cannabis. 

Of course, just carrying the CHRNA2 gene doesn’t make one a marijuana addict. A carrier might not even consume the drug. But the gene’s presence can increase the risk of addiction for those who do try cannabis, according to Demontis. 

“So just because you have the gene that we have identified, this doesn't mean that you get addicted to cannabis just by smoking it; it’s a complex disorder.”

Indeed, the disorder is so complex and under-studied that Demontis and her team aren’t even sure how their identified genetic marker actually induces addiction. Although they have ideas, that discovery, she explained, will be for other researchers to make. 

“The variant we identified is associated with a decreased expression of the nicotine receptor, which in the brain is associated with an upregulation of the cannabinoid receptor one gene,” she said. 

Type 1 cannabinoids receptors are found along the body’s nervous systems and can activate in the presence of cannabis compounds like THC and CBD. 

“And that's where we stop because I cannot claim more than what we can see,” she continued. “I'm a geneticist, so my field of expertise is the genome. Hopefully, some molecular biologist will take these findings and try to elucidate the biological mechanisms.”

And any future research will also need to take the study’s homogeneity into account. While hundreds of thousands of genomes were analyzed, those data were sourced from a relatively small group of northern Europeans. Taking note of the study’s limitations, Demontis has already made attempts to diversify her data for future research by including genomes supplied by US scientists, but more data from other researchers will be needed, too, before the findings will be fully accepted.

As cannabis legalization begins to make an effect in Canada and the US states that have enacted it, some fear that the incidence of CUD is likely to increase. However, one study from earlier this year found that adolescents living in more conservative states were more likely to abuse cannabis than their peers living in liberal states.

Putting that research into context, its lead author Morgan Philbin, an assistant professor of sociomedical sciences at Columbia University, commented that “while this research does not suggest that being in a liberal state causes people to use cannabis, or have lower rates of cannabis use disorder, it does highlight how states may differ beyond substance use policies, and how these differences also merit attention.”