Antipsychotics eased symptoms, but relapse-prevention evidence remains thin

BACKGROUND: Amphetamine- and cannabis-induced psychoses are common clinical presentations that are difficult to differentiate from primary psychotic disorders. However, there are limited guidelines around the appropriate use of antipsychotic medications to treat these disorders. This review examined the literature considering the optimal drug, dose and duration of antipsychotic therapy to treat and prevent relapse of amphetamine- and cannabis-induced psychoses. METHODS: A systematic review was conducted to identify original empirical studies considering antipsychotic drugs for the management of amphetamine- and cannabis-induced psychoses. Appraisal of included randomised controlled trials used the Cochrane risk-of-bias 2 and Joanna Briggs Institute critical appraisal tools, and the appropriate Joanna Briggs Institute tool for non-randomised controlled trials. Primary outcomes were measures of psychotic symptoms and rates of relapse of psychosis. Standardised mean differences were calculated where possible, and a narrative synthesis was completed. RESULTS: This review included 11 studies investigating amphetamine-induced psychosis, totalling 724 participants, and 4 studies investigating cannabis-induced psychosis, totalling 1872 participants. Aripiprazole, haloperidol, olanzapine, paliperidone, quetiapine and risperidone were associated with reduced psychotic symptoms in amphetamine-induced psychosis; however, no regimen was superior. Likewise, risperidone, haloperidol and olanzapine were associated with reduced psychotic symptoms in cannabis-induced psychosis. There was no data regarding relapse following antipsychotic treatment for amphetamine-induced psychosis, and limited evidence to guide practice recommendations regarding relapse prevention following antipsychotic treatment for cannabis-induced psychosis. CONCLUSIONS: This review found support for the effectiveness of antipsychotic drugs in reducing amphetamine- and cannabis-induced psychosis symptoms. However, a lack of studies including follow-up post-cessation of treatment meant that there is currently insufficient evidence to guide recommendations about which regimen is most effective at preventing relapse to psychosis.