The aim of this longitudinal study was to determine whether the depot formulation of an antipsychotic reduces violence in outpatients with schizophrenia as compared to oral administration of the same antipsychotic.

Forty-six previously violent patients with schizophrenia were randomised to receive treatment with oral or depot zuclopenthixol for 1 year. Clinicians interviewed patients at baseline and every month thereafter to assess treatment adherence. An interviewer blinded to treatment assignments interviewed an informant about any violent behaviour during the previous month.

Violence during the follow-up year was inversely proportional to treatment adherence, better compliance, and greater reduction of positive symptoms. Lower frequency of violent acts was observed in the depot group. The level of insight at baseline was not significantly associated with violence recidivism. Regardless of route of administration, treatment non-adherence was the best predictor of violence.

Some patients with schizophrenia and prior violent behaviour may benefit from the depot formulation of antipsychotic medication.