Epidemiological studies suggest that cannabis use has a negative impact on the expression and course of schizophrenia [48, 133, 143, 166, 167]. In contrast, studies based on self-report of subjective effects suggest that schizophrenia patients use substances such as cannabis to “self-medicate” negative symptoms, depression, and side-effects of antipsychotics, to relieve boredom, to provide stimulation, to “feel good”, to “get high”, or to “relax” and to socialize with peers [5, 51, 172, 192, 195]. However, these studies rely on retrospective self-report, and therefore are subject to denial and rationalization, both of which play a role in substance misuse disorders. Cannabis alters perception and has amnestic effects, both of which influence the recall of events. Further, since cannabis is often used in combination with other substances, sometimes without knowledge of the user, attributing certain effects solely to cannabis is difficult. Finally, it is possible that the positive and negative effects of cannabis may be dose-related, and this could be only crudely assessed in existing studies. The contrasting conclusions of self-report and epidemiological studies raise the possibility that schizophrenia patients may derive some immediate “benefits” from cannabis at the expense of later, negative consequences.
