What are the effects of Cannabis on Psychiatric Conditions?

With the increasing push to legalize cannabis in Western nations, there is a need to gage the potential impact of this policy change on vulnerable populations, such as those with mental illness, including schizophrenia, mood, and anxiety disorders. This is particularly important as there are strong motives in these individuals to seek short-term reward (e.g., "getting high"). Nonetheless, data to support the beneficial effects of cannabis use in psychiatric populations are limited, and potential harms in patients with psychotic and mood disorders have been increasingly documented.

Several studies have linked marijuana use to increased risk for psychiatric disorders, including psychosis (schizophrenia), depression, anxiety, and substance use disorders, but whether and to what extent it actually causes these conditions is not always easy to determine.

Post Traumatic Stress Disorder, or PTSD, is a prevalent, chronic, and disabling psychiatric condition that may develop following exposure to a traumatic event. If left untreated, the condition may persist for years. PTSD patients often re-experience their traumatic event and display avoidance behavior, emotional numbness, concentration problems, anger, irritability, hypervigilance, and suffer from insomnia. 

Treatment consists of psychotherapy and pharmacological intervention, but outcomes are often disappointing. It's interesting to point out that several lines of evidence point to possible involvement of the endocannabinoid system and particularly the CB1 receptors in the development and maintenance of PTSD. 

A recent review on PTSD and marijuana found no less than 46 articles directly addressing the question of efficacy of medical marijuana on PTSD symptoms. Lack of randomized controlled trials was also noted. Since most of these reports are observational in nature, they suggest a decrease in symptoms such as anxiety and insomnia, and affirm improved coping with marijuana use. On the flip side, increase incidence of cannabis use disorders among adults with PTSD was noted in a number of these reports. 

While cannabis may help PTSD patients, it has been shown that even temporary discontinuation can lead to withdrawal and aggravate PTSD symptoms. This also generates cannabis addiction. Despite these observations, medical cannabis has been approved for the treatment of PTSD in certain countries. 

Physicians are advised to use their own clinical judgment when weighting their potential risks and benefits of such a treatment for the patients on a case by case basis. Depression and chronic pain are tightly linked and likely share some of the same neurobiological mechanisms. Indeed, as we have mentioned earlier in this course, antidepressants can reduce certain types of pain. Given the large interest in cannabis for pain intervention, we naturally wonder if it can affect depression as well. 

Studies have shown a bi-directional effect of marijuana on depression. On the one hand, studies on patients with chronic pain demonstrated positive effect of medical cannabis on mood. Cannabis had the same effect on PTSD and other conditions as well. That said, given the coexistence of these conditions with depression, it is difficult to say if medical cannabis improves mood by relieving other symptoms or if it has a direct independent effect on depression. On the other hand, cannabis use, and especially early onset use, that is used in youth under the age 17, has shown an association with later onset of depression. A 2010 epidemiologic study gathered data from some 85,000 subjects from 17 countries participating in a population-based WHO World Mental Health Survey Initiative. 


After controlling for confounding factors, such as tobacco use and other mental health problems, the study showed a 1.5 increase in the risk for developing depression among marijuana users compared to non-users. This is considered a modest effect, but it was statistically significant and showed no gender differences. 

These results are further supported by another study published in 2015 where an association was found between early onset of cannabis use and the early onset of Bipolar Affective Disorder, also known as Manic Depressive Disorder, and suicide attempts. Bipolar Disorder, by the way, is associated with poor health outcome and is responsible for the highest rate of suicide among all mental disorders. We can conclude by saying that research points to a clear link between early cannabis use and later mental health problems, possibly in those with genetic vulnerability, and that there is a particular issue in the use of cannabis by children and adolescents.




Prof. Elon Eisenberg

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