Schizophrenia secondary to cannabis use

Facts box There are good theoretical reasons why cannabis may be a contributor to the development of schizophrenia. There is compelling evidence that cannabis use and psychosis are associated, and the debate is on whether cannabis use is a cause of psychosis. There is strong evidence from longitudinal studies that cannabis use may precipitate schizophrenia in vulnerable individuals. The vulnerability to cannabis-induced psychosis may be genetic, but further research is needed to support the preliminary evidence. There is also reasonable evidence that cannabis use exacerbates symptoms of psychosis in persons with a psychosis who continue to use cannabis. The evidence does not rule out the possibility that persons with psychosis use cannabis to control some of their symptoms or to improve their mood, but the self-medication hypothesis is unlikely to wholly explain the relationship observed between cannabis use and psychosis. Cannabis may promote psychosis directly through the cannabinoid system or indirectly through the dopaminergic system. More biological research on these mechanisms is necessary. Introduction There are good reasons for suspecting that regular cannabis use may be a contributory cause of schizophrenia. First, tetrahydrocannabinol (THC), the major psychoactive ingredient in cannabis preparations, can produce euphoria, distorted time perception, cognitive and memory impairments. Under controlled laboratory conditions, normal volunteers using THC in high doses have reported visual and auditory hallucinations, delusional ideas, and thought disorder.