Last year, Netherlands researchers reviewed five studies and concluded that the use of marijuana (cannabis) approximately doubles the risk of developing schizophrenia. Because the studies excluded anyone with a history of psychosis and controlled for the use of other drugs, they were "able to show the specific effects of cannabis."
Now a new study from the Albert Einstein College of Medicine in New York has shed light on the reason for the link between marijuana and schizophrenia. With several groups of adolescents as their subjects, they used a special type of MRI called diffusion tensor imaging to compare the brains of those with and without schizophrenia, both users and non-users of marijuana. They found that heavy use of marijuana caused the type of abnormalities in certain areas of the brain as were found in the brains of the subjects with schizophrenia, and these abnormalities were the most pronounced in schizophrenic subjects who regularly smoked marijuana. The abnormalities occur in a brain pathway related to language and auditory functions which is still developing during adolescence.
Thus if a young person is genetically at risk for schizophrenia, the research suggests, the use of marijuana can cause the same kind of damage the schizophenia would cause, which could bring on the illness when it might otherwise have not have emerged, cause earlier onset, and/or worsen the condition.
Newsday quoted one of the study's authors, Dr. Manzar Ashtari, as saying, ""Don't put yourself at risk, especially if you have a family history of schizophrenia or severe mental illness -- especially when the brain is still growing."