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Cannabis use strongly linked to mental disorders in a new study

Cannabis use, one of the most widely consumed illegal substances worldwide, could have a stronger connection to the onset of mental disorders than previously believed, according to new research.

This study offers a fresh perspective on the risk factors associated with Cannabis Use Disorder (CUD). It suggests that its repercussions might extend far beyond the widely accepted links to schizophrenia.

How the cannabis use study was conducted

The comprehensive study involves registry data from over six million individuals in Denmark. It presented compelling findings that CUD could amplify the risk of not only psychotic, but also non-psychotic depression and bipolar disorder.

Oskar Hougaard Jefsen, a PhD candidate from the Department of Clinical Medicine at Aarhus University, spearheaded this study. The findings have just been featured in JAMA Psychiatry, a prominent scientific journal.

“Upon accounting for variances in gender, age, socioeconomic status, family history, and more, it becomes clear that CUD is tied to almost double the risk of developing depression, and two to three times the risk of developing bipolar disorder, for both sexes,” notes Jefsen.

Despite one in three Danes under 25 having smoked marijuana as per the Danish Health Authority, this study zeroes in on those with substantial marijuana consumption leading to a substance use disorder diagnosis. This typically includes individuals who have engaged with the substance abuse treatment system or other health care services.

Few studies have explored this mental health connection

While the consensus among various studies is that heavy marijuana use can adversely affect mental health, the comprehensive exploration of its connection to other mental disorders had been sparse. This newly published study fills this gap, offering new insights into the potential risks of cannabis use.

The research teams from Aarhus University and the University of Copenhagen meticulously analyzed data from Danish nationwide registers. These included the National Patient Register, the Danish Psychiatric Central Research Register, and the Danish Register of Pharmaceutical Sales.

Jefsen calls the study the most extensive of its kind globally. He stated, “Our findings suggest that CUD is also associated with an increased risk of developing depression and bipolar disorder. Our results recommend caution in cannabis use, especially for those at higher risk of mental illness and decision-makers contemplating cannabis legalization.”

More and more nations are legalizing cannabis use

The past few years have seen a rising number of nations legalizing marijuana for medicinal and recreational purposes. Since 2018, general practitioners in Denmark can prescribe cannabis-based drugs. This opened avenues for companies and individuals to produce cannabis for medicinal or industrial use.

However, Jefsen believes the study’s findings must be factored into any future legislation and control measures around cannabis use. Calling for additional research, Jefsen emphasized the need to identify those particularly vulnerable to the negative impacts of cannabis.

He believes this could enhance preventative measures and necessitates further exploration into the dose-dependent effects of cannabis on cognition, behavior, and the brain. Moreover, determining the risk factors that cause a shift from CUD to psychiatric disorders is also paramount.

Study’s results are not conclusive, more research is needed

Despite the compelling indications, the study does not conclusively assert that cannabis triggers these mental disorders. Jefsen recognizes the possibility that undiagnosed depression or bipolar disorder may lead some individuals to develop CUD. This suggests that the disorder might be a consequence, rather than a cause, of cannabis abuse.

Yet, he insists that self-medication cannot be the sole explanation, especially considering the heightened disease risk persisting a decade after CUD diagnosis. “The likelihood of a vast number of people remaining undiagnosed for such an extended period seems improbable,” he asserts.

Jefsen applauds the unique insights offered by Danish registry data. However, he underscores that a randomized controlled trial would be required for definitive evidence. He also cautions against such a study, deeming it unethical. According to Jefsen, it would necessitate participants smoking large amounts of cannabis to determine long-term mental health risks.

As we navigate the evolving landscape of cannabis use, these insights underscore the importance of approaching policy changes with caution. As Jefsen points out, legalization and control measures should consider the potential risks associated with heavy marijuana use.

Above all, understanding the potential implications of cannabis use on mental health is of utmost importance, whether it is for individual users, healthcare professionals, or policymakers.

More about cannabis

Cannabis, also known as marijuana, is a plant that has been used for various purposes for thousands of years. It is perhaps most well-known for its psychoactive properties, which can alter the user’s mental state, leading to feelings of euphoria, relaxation, and altered perception.

Botanical Information

Cannabis is a genus of flowering plants in the family Cannabaceae. The number of species within the genus is disputed, but it is generally accepted that it consists of at least three species: Cannabis sativa, Cannabis indica, and Cannabis ruderalis.

Cannabis plants produce a group of chemicals called cannabinoids, which generate mental and physical effects when consumed. The two most well-known of these are delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD).

THC is the primary psychoactive compound in cannabis, responsible for the high sensation. CBD, on the other hand, is not psychoactive and is being studied for its potential therapeutic uses, including in the treatment of epilepsy, pain, and various mental health conditions.


Historically, cannabis has been used for various purposes, including medicinal, religious, and recreational. The plant has also been used to produce hemp, a variety of Cannabis sativa that has a very low THC content and is used to produce a wide range of products, including textiles, paper, and biodegradable plastics.

In recent decades, medical cannabis, which refers to the use of the cannabis plant and its components to treat diseases or conditions, has gained recognition. Some jurisdictions have legalized its use for treating a range of conditions such as chronic pain, multiple sclerosis, and cancer-related nausea.

Recreational cannabis use is also legal in certain parts of the world, including several states in the US, Canada, and Uruguay. However, it remains illegal in many countries and can be associated with legal penalties.

Effects and Risks

The effects of cannabis use can vary widely, depending on a variety of factors, including the strain of cannabis, the method of consumption, the user’s tolerance, and their physical and mental state at the time of use. Effects can include feelings of euphoria, relaxation, altered perception, and increased appetite. Some people may also experience negative effects, including paranoia, anxiety, and panic attacks.

There are also several health risks associated with cannabis use, particularly heavy use. These include an increased risk of mental health disorders, such as depression, anxiety, and some forms of psychosis. There is also evidence that regular, heavy cannabis use can lead to cognitive impairment, particularly in those who begin using cannabis at a young age.

Furthermore, smoking cannabis can lead to respiratory problems, similar to those caused by smoking tobacco. Cannabis can also be addictive, leading to cannabis use disorder, which is characterized by an inability to stop using the drug despite it causing harm to one’s life or health.

While research into cannabis and its potential uses and harms is ongoing, it’s clear that, like any drug, it can have both positive and negative effects, and its use should be approached with caution. As with any substance, it’s essential to be informed and mindful about its potential effects and risks.

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