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Question:

I've read that new research has shown marijuana use can cause schizophrenia in people with a predisposition for this brain disorder. The subtype, disorganized schizophrenia, especially. Why is this?

Answered by: Margaret Haney

The vast majority of people who smoke marijuana do not develop psychosis. However, recent research has shown that individuals with a certain set of genes are vulnerable to the effects of marijuana on mental health.

Specifically, individuals with a variation of a gene regulating brain dopamine levels who smoked marijuana as adolescents (by age 15) were much more likely to develop psychosis as adults than (a) individuals without this genetic vulnerability, or (b) individuals who had the genetic vulnerability but who did not smoke marijuana as adolescents.

It is not clear why marijuana affects this vulnerable population in this way, but it is likely due to marijuana’s effects on dopamine regulation.

Schizophrenia is associated with disturbances in brain dopamine . During adolescence, the brain is developing rapidly. It may be that for a vulnerable group, a drug of abuse like marijuana has more profound effects on the regulation of dopamine during this time of development than in later years.