Impact of cannabis use and its cessation on the dosage and the efficacy of antipsychotic drugs in in- and outpatients with schizophrenia taking medication: A systematic review and meta-analysis.

Compared with the general population, there are more cannabis users among patients suffering from schizophrenia and this consumption seems to impact the course and the treatment of their pathology. The aim of this meta-analysis and systematic review was to assess the impact of cannabis use on the efficacy of treatments, more particularly regarding the antipsychotic dosage, symptoms evolution, therapeutic resistance and the risk of relapse in patients with schizophrenia taking medication. We performed a systematic search of keywords on multiple databases up to August 2020 to identify all studies meeting the following criteria: comparison between cannabis smokers and non-cannabis users in patients with schizophrenia, assessment of antipsychotics doses, information about their efficacy or resistance to treatment and control of the compliance. Standardized mean differences were calculated for antipsychotic dosage and symptoms evolution at discharge, and a systematic review was performed for other outcomes. Twelve studies were included. Cannabis use did not seem to be associated with higher doses of antipsychotics at seven days and at the end of the studies, nor with poorer symptoms evolution, and nor with higher rate of antipsychotic resistance. However, cannabis use seems to be associated with a higher risk of relapse. This meta-analysis provides evidence that previous cannabis use, or occasional use, in patients with schizophrenia taking medication does not impact antipsychotic efficacy as described by antipsychotic dosage or PANSS score.