“By studying the biological underpinnings of why someone may use cannabis to then lead to disorder, this will reveal something fundamental and can lead to new therapeutics,” Sanchez-Roige, a researcher at the UCSD Institute for Genomic Medicine, said in an interview.
For example, genomic data could identify existing drugs that might be useful to treat cannabis use disorder, researchers said.
A cannabis use disorder is not as deadly as an addiction to opioids or alcohol can be. It can still disrupt people’s daily lives, interfering with a person’s work, education and relationships, and some struggle to quit because of nausea and mood swings.
There is no Food and Drug Administration-approved medication specifically to treat cannabis use disorder.
Scientists have long known that genetics alongside environmental factors play a substantial role in addiction to substances but caution that more studies are needed.
Thousands of genetic traits may affect a person’s vulnerability to addiction - and even then, the risk of getting hooked may only be slightly higher, said Wayne Kepner, an addiction researcher at Stanford University who was not involved in the UCSD study.
He said studies are unlikely to find a single gene - or even a cluster of genes - that causes addiction.
“The brain is too complex, and addiction is not just biological or neurochemical,” he said.
“It’s deeply influenced by context, stress, and social environment.”
Real-world payoff from genome and addiction research remains far off, researchers cautioned, and developing tests to figure out who is predisposed to addiction has proved a thorny issue.
Genetics researchers have criticised the FDA’s 2023 decision to approve a test that purports to assess the genetic risk of opioid addiction, asserting the test relied on unsound science.
Twenty-four American states have legalised recreational marijuana. The drug’s use, including in forms that are highly potent and easier to use repeatedly throughout the day, has proliferated across age groups.
That has raised concern from public health advocates, addiction experts and lawmakers about stronger, poorly regulated cannabis products with harmful effects.
In 2024, an estimated 64.2 million people had used cannabis during the previous year, according to an annual federal survey. That’s up from an estimated 53.2 million three years earlier.
The survey also reported that, in 2024, an estimated 20.6 million people had a cannabis use disorder, defined as a spectrum of problematic use that can cause distress or interfere in one’s daily life. That’s also an increase from previous years.
Recent research into the human genome has offered tantalising clues into the genetic patterns of people who use - and sometimes abuse - marijuana.
In the new study, researchers at UCSD examined genetic data from nearly 132,000 clients of 23andMe who responded to surveys about their cannabis use.
One of the genes associated with cannabis use identified by UCSD researchers is involved in brain development and communication between neurons and has been linked to psychiatric disorders such as schizophrenia.
Study co-author Abraham Palmer stressed that the association does not mean cannabis causes schizophrenia.
“It’s just that there’s some biological pathways that may be in common across cannabis and schizophrenia,” said Palmer, a UCSD researcher.
Another gene is involved with signalling between nerve cells, particularly in the brain, and has been linked in previous studies to impulsive personality, obesity, and cancer metastasis.
The gene has also been associated with frequency of cannabis use, researchers said.
A secondary analysis revealed an additional 40 genes associated with cannabis use during one’s lifetime and four linked to frequency of the drug’s use. The paper said 29 of these genes had not previously been associated with “cannabis-related traits”.
Researchers emphasise that a genetic association does not necessarily mean a gene causes a condition.
A Yale study published this month found a correlation between cannabis use during one’s lifetime and genetic traits “related to openness to experience and risk-taking, including substance use and sexual behaviours”.
An earlier Yale-led analysis of the genomes of more than a million people, many of them military veterans, found that certain variants of genes were associated with elevated risk of developing cannabis use disorder.
Those variants were also associated with an elevated risk of developing lung cancer, although Yale researchers Daniel Levey and Joel Gelernter said more research was needed to parse out the effects of tobacco use or other factors.
Gelernter, in an interview, noted that genetic differences between people who casually use marijuana and those who develop a disorder amount to a statistically important amount of risk - but too small for real-world applications.
“It’s not something that is yet even approaching clinical utility,” Gelernter said. “Although it may someday.”
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