The same genes are related to both cannabis use and severe mental disorders

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A new study indicates that some individuals are more prone to both cannabis use and developing mental disorders, such as schizophrenia and bipolar disorder, than others.

The relationship between cannabis use and psychiatric disorders has been widely debated.

Cannabis is a psychoactive and addictive drug that sometimes produces symptoms similar to psychosis.

Psychiatric disorders such as schizophrenia and bipolar disorder are characterized by a severely disturbed perception of reality or a state of confusion.

In a new study published in Psychiatry lancetresearchers have shown that there are shared genetic factors underlying our susceptibility to both cannabis use and some psychiatric disorders.

These findings could indicate that a subset of the population is at high risk for both cannabis use and some psychiatric disorders, based on their genetics, Weiqiu Cheng says.

She was the study’s first author along with Nadine Parker. At the time of the study, they were both researchers at the Norwegian Center for Research on Mental Disorders (NORMENT), a center of excellence at the University of Oslo.

Our genetics play an important role

Individuals who use cannabis are at a threefold risk of developing psychosis. Permanent use of cannabis can also lead to the development of bipolar disorder.

We know that genetic factors influence an individual’s likelihood of using cannabis. We also know that genetic factors play an important role in determining an individual’s susceptibility to developing psychiatric disorders, Cheng says.

Genetic variants are differences in the DNA code between different individuals. When we talk about genetic variants associated, for example, with a particular psychiatric disorder such as schizophrenia, it indicates that this variant can increase or decrease a person’s risk of developing that particular disorder.

Previous research has shown that some of the genetic variants associated with cannabis use are also linked to psychiatric disorders, Cheng says.

In other words, there is a genetic link between cannabis use and some psychiatric disorders. The NORMENT researchers wanted to explore this genetic link further with this study.

Explain why some are more susceptible than others

The study helps explain why some individuals are more susceptible to both cannabis use and certain psychiatric disorders, says Nadine Parker, a postdoctoral fellow at NORMENT.

Because not only is there a link between genetic variants. In reality, it is the same genetic variants that cause a person’s susceptibility to both cannabis use and the development of psychiatric disorders, such as schizophrenia and bipolar disorder.

These findings are important as they show that the complex links between cannabis use and these disorders may not only be caused by cannabis use itself, but could also be driven by a shared genetic susceptibility, Parker explains.

Preventive measures are needed

We may use study information to develop preventative measures for people at high risk. This could, for example, reduce cannabis use among people with a high genetic risk for schizophrenia and bipolar disorder, Cheng says.

Information about shared genetic variants can also help develop more targeted therapeutic efforts.

Our better knowledge of genetic overlap could be used to stratify patients for more specialized treatment plans, Parker says.

Some genetic variants have opposite effects on cannabis use and psychosis

The study results showed that the majority of shared genetic variants increase the risk of both cannabis use and the development of schizophrenia or bipolar disorder.

However, NORMENT researchers have also found some genetic variants with the opposite effect on cannabis use and mental disorders.

We also found genetic variants that increase the risk of cannabis use, while also reducing the risk of the two psychiatric disorders. This finding suggests a complex relationship, Cheng says.

Could cannabis be a potential treatment for psychosis?

Cannabis is used medicinally for pain relief and as an antidepressant in some regions of the world. A component of cannabis is also considered to be a potential treatment for psychosis.

Among patients with psychosis-related disorders, such as schizophrenia and bipolar disorder, the rate of cannabis use is higher than in the general population.

Shared genetic variants with opposing effects may suggest the presence of biological mechanisms that could support the beneficial effects of cannabis, the researchers point out.

Advanced statistical methods were used in the study

To explore the genetic association between psychotic disorders and cannabis use, NORMENT researchers used advanced statistical models.

We leveraged the latest genetic evidence for cannabis use, schizophrenia and bipolar disorder in analyzes using state-of-the-art methods that assess genetic overlap, causality and prediction, Parker says.

The analysis was based on the results of previously conducted genome-wide association studies in schizophrenia, bipolar disorder, cannabis use disorder, and lifetime cannabis use.

Combined, these studies included over 1 million participants. Genetic information from these previous studies was used to conduct the current analyses.

Reference:

Cheng et al. “The Relationship Between Cannabis Use, Schizophrenia, and Bipolar Disorder: A Genetically Informed Study,” Lancet psychiatry, vol. 10, 2023. DOI: 10.1016/S2215-0366(23)00143-8 (Summary)