Longitudinal studies suggest that marijuana use is a significant risk factor in the development of schizophrenia. While individuals with schizophrenia are more likely to use marijuana, research indicates a potential causal relationship rather than just a correlation. The risk increases substantially with more frequent use. However, marijuana use is not considered an essential or sufficient cause, as not all individuals with schizophrenia have used it, and most users do not develop the disorder. The evidence suggests that marijuana use may play a role in triggering the illness, particularly in individuals who already have an underlying vulnerability.