Chronic cannabis use significantly increases the risk of mental health problems and personality disorders, according to a large study.
A study of more than 6.6 million people in Denmark found that those addicted to marijuana were four times more likely to develop major depression or bipolar disorder.
They looked at people with cannabis use disorder (CUD), defined as an inability to stop using the drug even when it harms their health and social life.
In recent decades, the incidence of depression has been increasing, which is associated with increasing and aging. But the researchers warned that it could become more common as marijuana becomes legal. It can be used recreationally in 22 US states.
The analysis of 6.6 million people showed that long-term cannabis smoking increased the risk of psychotic bipolar disorder by 4.1 times and any depression by 1.8 times.
The researchers found that 14 percent of people with cannabis use disorder later developed bipolar disorder.
Researchers at Aarhus University Hospital in Denmark analyzed medical records of people born between 1995 and 2021.
All participants were at least 16 years old. All were from Denmark, where recreational cannabis use is illegal but still available on the black market.
Participants’ medical records were checked for cannabis use disorder, history of major depression, psychotic features, and nonpsychotic and bipolar disorder with psychotic features.
Major depression is defined as low or no interest in previously enjoyed activities for more than two weeks.
Bipolar disorder is an illness that causes mood swings ranging from depressive lows to manic highs.
Psychotic features such as delusions, hallucinations, incoherent talking, and irritability can accompany both disorders.
About 56,000 participants had a cannabis use disorder.
41 percent of these people were diagnosed with major depression. Almost all (96 percent) of those diagnoses were for psychotic major depression.
The risk of major depression was high after a diagnosis of cannabis use disorder, but ‘significantly increased five to 10 years after CUD,’ the researchers said.
About 56,000 participants had a cannabis use disorder. 41 percent of these people were diagnosed with major depression
Almost all (96 percent) major depression diagnoses were non-psychotic depression.
The findings are consistent with previous studies that have shown a significant link between cannabis use and depression, but not bipolar disorder.
They also found that 14 percent of people with cannabis use problems later developed bipolar disorder.
Again, most patients (90 percent) had psychotic bipolar disorder.
Cannabis use disorder is associated with an increased risk of any form of bipolar disorder in men, with men three times more likely than women.
This was similar for psychotic bipolar disorder, with male chronic cannabis users three times more likely and female users 2.6 times more likely to be diagnosed.
The findings are consistent with previous studies that have shown a significant link between cannabis use and depression, but not bipolar disorder.
The results indicate a ‘mainly psychotogenic effect of cannabis’, meaning its ability to induce psychotic reactions that can include confusion, depression and hallucinations.
Tetrahydrocannabinol (THC), the main psychoactive component of cannabis, acts on cannabinoid receptors and is thought to increase psychotic risk by disrupting the normal functioning of the part of the brain that processes information and determines behavior.
‘There is no consistent model of how cannabis affects the development of affective disorders,’ the researchers said.
There is also a lack of evidence that stopping cannabis use can reduce the risk of developing mental disorders, he said.
Their findings demonstrate the need for improved knowledge of the dose-dependent effects of cannabis use on the brain, cognition and behavior, and have implications for the legalization of cannabis, they said.
The study was published in the journal JAMA Psychiatry.
Several studies have found a link between cannabis and schizophrenia in the past, although the exact cause remains unclear.
Marijuana causes psychological problems, affecting the way you think, make decisions, handle emotions, and interact with reality.
It can also interfere with brain development in young people.
But people who are schizophrenic can easily use cannabis to relieve their symptoms.