Does using cannabis increase the risk of depression and bipolar disorders?

Cannabis is one of the most commonly used substances in the world. In 2021, 13% of Americans reported past 30-day use of cannabis, making it the most-used federally illegal substance in the US.

While many people use cannabis occasionally, such as socially or recreationally, approximately three in ten cannabis users develop Cannabis Use Disorder (CUD). The risk of CUD is most significant for those who begin using cannabis before age 18.

Cannabis affects the parts of the brain responsible for memory, learning, attention, decision-making, and emotion. Cannabis may have psychotogenic effects, meaning it can cause psychotic disorders. The psychoactive component of cannabis, THC, may increase the risk of psychosis. Long-term cannabis use is also linked to an increased risk of schizophrenia. However, there is still much to learn about cannabis use and the risk of other mental disorders.

A new Danish study aimed to determine if there is a relationship between CUD and affective disorders, which include psychotic and non-psychotic depression and bipolar disorders.

What is Cannabis Use Disorder (CUD)?

CUD refers to a behavioral and/or chemical addiction to cannabis. Cannabis is an addictive substance, and most people diagnosed with CUD are addicted to cannabis. Those with CUD may experience cravings for cannabis, withdrawal if they go without cannabis, and prioritizing cannabis use over work, relationships, and hobbies.

Someone with CUD uses cannabis despite it causing harm to themselves or others. They cannot stop using cannabis even though it negatively impacts their life and health.

Unfortunately, drinking alcohol before or during an attempt to quit smoking is one of the most common reasons that smoking cessation attempts fail.  Experts often recommend that people trying to quit smoking avoid alcohol for the first few weeks, as it can trigger an intense craving for a cigarette. Quitting smoking can temporarily heighten stress and tension, and alcohol is known anecdotally to reduce tension, which may be one reason why people drink more when trying to quit smoking. In addition, tobacco addiction is as much a behavioral addiction as a physiological addiction. For those who drink and smoke concurrently, such as in social situations, drinking becomes near-impossible without the addition of a cigarette.

What did this study do?

This cohort study followed over six million people with and without CUD living in Denmark between 1995 and 2021. The study aimed to analyze whether CUD was associated with a subsequent diagnosis of depression or bipolar disorders. This information was gathered using databases from hospitals and national patient registries.

The researchers were interested in understanding the potential psychotogenic effects of cannabis, so they further analyzed the data by dividing patients with psychotic and non-psychotic depression and bipolar disorders.

What were the main findings?

CUD was found to be associated with later diagnoses of both depression and bipolar disorders. In total, 0.9% of the population studied received a diagnosis of CUD and 3.9% were diagnosed with an affective disorder.

40.7% of individuals diagnosed with CUD were later diagnosed with depression. Expressed in terms of risk, individuals diagnosed with CUD had an 84% higher risk of being diagnosed with depression than those without CUD. Most of these diagnoses (96%) were for non-psychotic depression. There were no differences seen in depression diagnoses between men and women.

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14.1% of individuals with CUD later received a diagnosis of bipolar disorder, which translates into nearly three times higher risk of bipolar disorder for people with CUD. Of these, 90% were for non-psychotic bipolar disorder. In addition, the risk of any bipolar disorder was 42% higher among men than women.

Although fewer people with CUD were diagnosed with bipolar disorder than with depression, the relative risk of bipolar disorder was higher. Those with CUD were nearly three times as likely to be diagnosed with non-psychotic bipolar disorder and four times as likely to be diagnosed with psychotic bipolar disorder.

The increased risk for both depression and bipolar disorder was highest in the six months immediately following one’s CUD diagnosis, but it remained elevated for up to 10 years.

What are the key takeaways?

Those diagnosed with Cannabis Use Disorder (CUD) are more likely to be later diagnosed with psychotic or non-psychotic depression or bipolar disorder, with the highest risk being for psychotic bipolar disorder. These risks are most elevated for the first six months following a diagnosis of CUD.

Based on the information from this study and the association of cannabis use with schizophrenia, the evidence suggests that cannabis has some psychotogenic effects. Therefore, the researchers suggest investing in public education campaigns to reduce cannabis use. However, more research is needed to determine if cannabis cessation will help people with affective disorders.

References

Jefsen OH, Erlangsen A, Nordentoft M, Hjorthøj C. Cannabis Use Disorder and Subsequent Risk of Psychotic and Nonpsychotic Unipolar Depression and Bipolar Disorder. JAMA Psychiatry. Published online May 24, 2023. doi:10.1001/jamapsychiatry.2023.1256

Center for Disease Control and Prevention. Marijuana and Public Health. Addiction (Marijuana or Cannabis Use Disorder).https://www.cdc.gov/marijuana/healtheffects/addiction.html#:~:text=Some%20people%20who%20use%20marijuana,marijuana%20have%20marijuana%20use%20disorder.

Center for Disease Control and Prevention. Marijuana and Public Health. Data and Statistics. https://www.cdc.gov/marijuana/data-statistics.html