There is no compelling evidence that cannabis causes some psychiatric disorders in otherwise healthy individuals. Most tellingly, rates of schizophrenia and other psychiatric illnesses have remained flat even during periods of time when cannabis use rates have increased.

Patient Age and History

Part of the reason it’s so difficult to detangle psychoactive substance use from mental health is age of onset. For most people, symptoms of mental disturbance occur in the late teens and early 20’s.

Teens are also more likely to experiment with cannabis and less likely to be open with their parents about their drug use and/or any symptoms of mental disturbance they may be experiencing.  As a result, drug and alcohol use has usually already started by the time symptoms of mental illness become noticeable.

This is why we see so many studies that confirm most people diagnosed with severe mental illness have a history of alcohol and/or drug use. The alcohol and drug use was not the cause of the mental illness, however, but rather a behaviour that coincides with the undetected development of mental health symptoms.

Cannabis as Treatment

Research suggests that those with mental illness might actually be self-medicating with cannabis – turning to the plant to help manage their symptoms, rather than becoming ill after use.

Emerging evidence indicates that psychiatric patients who try cannabis show significant improvements in symptoms and clinical outcomes (such as lower mortality rates and better cognitive functioning) compared with those who have not.

And some of the unique chemicals in cannabis, such as cannabidiol (CBD), seem to have antipsychotic properties. Now, researchers are investigating it as a possible treatment for schizophrenia and depression.