Much ink has been spilt and many trees sacrificed debating the links between smoking cannabis and schizophrenia. Researchers from Stony Brook University in New York have added to the debate with a long-term study following 229 patients for ten years after they were first admitted to a psychiatric hospital. They compared the patients' use of marijuana - both recently and over their lifetimes - with how old they were when their symptoms started and how severe those symptoms currently were. Two-thirds of the participants had smoked cannabis at some point in their lives. The people who had used cannabis before being hospitalised had worse symptoms of psychosis than those who hadn't and were admitted at a younger age. Patients whose symptoms had become worse said they were smoking more cannabis next time they were interviewed and people who started smoking more cannabis developed worse symptoms.
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