An analysis of more than 14,500 people has shown that some genes increase the risk of cannabis dependence (CAD), according to a new study published in the JAMA Psychiatry journal.

The study authors say that marijuana is one of the most abused drugs after nicotine. This year, there have been stronger calls for cannabis to be legalized but many states have only allowed medical marijuana use for specific conditions. The Yale led study has also uncovered a link between marijuana dependence and other mental health problems.

Senior author of the study, Dr. Joel Gelernter, the Foundations Fund Professor of Psychiatry, professor of genetics and of neuroscience at Yale University School of Medicine, said, “We were surprised to find a genetic risk overlap between cannabis dependence and major depression.”

Details of the Cannabis Dependence Study

The National Institutes of Health (NIH) partly funded this Yale-led study that included Dr. Gelernter; Prof. Richard Sherva from Boston University School of Medicine, Boston, Massachusetts; Dr. Henry Kranzler from Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia and Mental Illness Research Education and Clinical Center, Veterans Affairs (VA) Stars and Stripes Healthcare; and other researchers.

More funding was provided by the Veterans Affairs Connecticut Healthcare Center, and the Philadelphia Veterans Affairs Mental Illness Research, Education and Clinical Center.

Study participants were drawn from three existing and independent substance dependence studies: the Yale-Penn Study, Study of Addiction: Genetics and Environment (SAGE), and International Consortium on the Genetics of Heroin Dependence (ICGHD).

The total number of participants was 14,754 and had a mean age of 39.2 years. Their genomes were analyzed and the researchers were able to identify several genes linked with major depression and schizophrenia. The researchers said there was a “genetic overlap” between CAD and these two mental illnesses.

Prevalence of Cannabis Use and Dependence

According to the National Institute on Drug Abuse (NIDA), marijuana use has increased over the years especially among young people. Despite the classification of marijuana as a dangerous drug, NIDA found that many people no longer see it as risky to use.

In 2007, the NIH published a report which showed that “9 percent” of people who used marijuana became dependent as compared to “15 percent of people who try cocaine and 24 percent of those who try heroin.” The researchers also found that marijuana use disorders were increasing among all age groups.

Once marijuana dependence takes root, it can eventually become an addiction thereby interfering with a person’s daily life. Those addicted to marijuana can experience withdrawal symptoms, tolerance to low amounts of cannabis, lack of control and responsibility, and suffer cognitive impairments.

While many cannabis legalization proponents will refute any information that goes contrary to the ‘marijuana is safe’ mantra, it is important to conduct more research to ensure that everyone stays safe and healthy.

As Dr. Gelernter told Live Science, “We hope our findings help bring more awareness to the public that cannabis use is often not benign and can lead to dependence, especially in individuals at high genetic risk.”