Cannabis and Mental Health

Cannabis consumption has been a worldwide phenomenon for centuries, long before its prohibition in the mid 1920’s. Yet our understanding of how cannabis affects users remains quite limited, as research has been thwarted in this area. Cannabis use is currently quite prevalent and in this blog we will take a look at a four research studies that look at the relationship between cannabis use and mental health.

A study following 1395 teens age 14-17 years in Munich Germany from 1995 for over 10 years found that the prevalence of cannabis use was 19.3 % at the beginning of the study and the prevalence of cannabis use disorder (more heavy use causing disruption of function) was 2.6%.  Ten years later the cannabis use prevalence increased to 54.3% and cannabis use disorder to 13.7%.  The study noted that the average onset of use was at 15 years of age.  The study also noted that certain mental health conditions such as bipolar disorder, other mood disorders and to some anxiety disorders contributed to the likelihood of increasing cannabis use and cannabis use disorder (1).

Another study noted that 33% of the cannabis using group were diagnosed with alexithymia, or difficulty with expressing and naming emotions.  So alexithymia may be a predisposing risk factor and efforts to encourage learning to talk about emotions in psychotherapy and at home may play an important role in reducing the risk for cannabis abuse in vulnerable individuals (2).

So based on the two studies above mood disorders, certain anxiety disorders and alexithymia can contribute to initiating cannabis use.

What about cannabis use in individuals already diagnosed with a psychiatric disorder?  A meta analysis of six articles, with 2391 individuals as sample, and an average follow up of 3.9 years looked at cannabis use in persons with prior diagnosis of bipolar disorder. The study found that cannabis use can contribute to worsening of bipolar disorder symptoms and a three times increased risk of developing another manic episode. These findings strongly suggest caution with cannabis use in people with prior history of bipolar disorder. (3)  

Another study looked at the link between cannabis use in teens and risk for developing schizophrenia type symptoms and depression by age 26.  The study divided the 1037 subjects into three groups, group that used cannabis at least three times by age 15, the second group reported use by age 18 and the third group served as control and reported either never using cannabis or once or twice by age 18.  The results showed that while there was no link between cannabis use and depression by age 26, for psychosis there was a four times increase in likelihood of psychotic symptoms by age 26 in the group that reported use by age 15.  Yet when the researchers excluded from this group individuals with some psychotic spectrum symptoms by age 11, this association became so small that it was no longer statistically significant (4).  This study suggests a need for caution, yet the results are not definitive at this point. 

The available research is limited and while we know that cannabis use is very common and starts early in life, we do not fully understand what impact it may have on brain development and how it affects existing mental health conditions or the risk of development of new ones. The available research data suggest a need for caution with cannabis use in teens with prior diagnosis of mental illness or strong family history of bipolar and schizophrenia.