Cannabis use and mental illness link found

By Dr. Ananya Mandal, MDAug 29 2018

A large new study has found that people with mental ailments such as schizophrenia are more genetically inclined to use cannabis.

The report of the latest new study titled, “GWAS of lifetime cannabis use reveals new risk loci, genetic overlap with psychiatric traits, and a causal influence of schizophrenia,” appears in the journal Nature Neuroscience this week. Professor Eske Derks from Queensland's QIMR Berghofer Institute and colleagues from different institutes across the world found that there are 35 genes that can influence a person’s propensity to use cannabis.

Apart from Queensland's QIMR Berghofer Institute, researchers from Radboud University in the Netherlands and Virginia Commonwealth University in the United States were also part of this study. The team for this study used DNA samples from more than 180,000 people from around the globe via 23andMe, the UK Biobank and 16 other study databases to come to their conclusions. They used an analysis technique called “Mendelian randomisation” to assess the connection between schizophrenia and an increased risk of cannabis use.

Marijuana leaves, cannabis on a dark background, beautiful background, indoor cultivation. Image Credit: Yarygin / Shutterstock

According to Professor Derks, there is a genetic overlap between those who use tobacco and other substances and the risk of developing schizophrenia and bipolar disorder. He explained, “In other words, the genes that increase the likelihood of cannabis use also influence these other traits and conditions.”

According to Prof. Derks, there have been numerous speculations associating cannabis use and mental illnesses but this is the first study that provides conclusive proof of the connection. The earlier studies he noted have said that cannabis is responsible for aggravating underlying mental ailments. This could mean that the previous researchers suggested that those with schizophrenia use cannabis to “cope with the symptoms”. Derks explained. This new study shows that “cannabis use could also contribute to the onset of schizophrenia.” They would need more evidence to support the study, he added though.

Professor Derks adds that cannabis as such is harmless but addiction may be seen in one in ten users. These genes could raise the risk of getting addicted he said. Certain personality types and risk takers have been seen to be more likely to start using cannabis. They noted that these same genes were also responsible for alcohol and tobacco dependency. These genes also showed up in individuals with autism, bipolar disorder, Attention Deficit and Hyperactivity Disorder (ADHD) and depression he explained. Strongest associations were seen in the CADM2. Jacqueline Vink of Radboud University, and the study's lead author explained that this gene has been associated with “risky behaviour, personality and alcohol use.”

Authors wrote, “Cannabis is a widely used psychoactive substance and its use is associated with various adverse mental health outcomes, including psychosis and schizophrenia. Successful prevention intervention efforts aimed at reducing cannabis use and misuse... require a better understanding of why some people use cannabis whereas others do not.

According to the team of researchers, they are trying to find how genes influence the frequency and amount of cannabis use among these individuals. This is till date, the largest genetic study on cannabis use and genetics, the authors add.