Cannabis, nicotine and the negative symptoms of schizophrenia: Systematic review and meta-analysis of observational studies

Despite the high prevalence in patients with schizophrenia, the association of cannabis and nicotine use with negative symptoms remains unclear. We performed a meta-analysis of observational studies addressing the association of cannabis and nicotine use with negative symptoms. Twenty cannabis studies (n = 2611) and 45 nicotine studies (n = 8942) were analyzed. There was no significant effect for current cannabis use alone or in combination with...