Thanks in part to the Netherlands' policy of marijuana decriminalization, there are people living in the Dutch city of Utrecht whose addiction to cannabis prevents them from getting effective treatment for mental illness. According to a September 10 statement from Utrecht Mayor Wolfsen, "There is a group of about eighty people with a chronic psychotic disorder who barely respond to their treatment. A possible explanation for this is their severe dependence [on] cannabis."
Cannabis is associated with psychosis (a symptom) and schizophrenia (an illness where this symptom is persistent) in complex, contradictory and mysterious ways. The evidence does demonstrate various links that we all should all be aware of, especially cannabis users and parents. However, the evidence does not support anything like the level of fear propagated in the media.
Experts at the Institute of Psychiatry in London are publishing research suggesting that smoking cigarettes may be a contributory cause of schizophrenia (a psychotic disorder). These new findings raise a question - could the most obvious fact about cannabis - that it is usually consumed in combination with tobacco - have been neglected in researching the link between cannabis and psychosis?
New research from Harvard Medical School, in a comparison between families with a history of schizophrenia and those without, finds little support for marijuana use as a cause of schizophrenia. “The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself,” note the researchers.
Cannabis dependence is a disorder primarily experienced by young adults, especially in higher income countries. It has not been shown to increase mortality as opioid and other forms of illicit drug dependence do. Our estimates suggest that cannabis use as a risk factor for schizophrenia is not a major contributor to population-level disease burden.