Risperidone as add-on therapy in behavioural disturbances in mental retardation: a double-blind placebo-controlled cross-over study.

A double-blind placebo-controlled cross-over trial was carried out to evaluate the efficacy and safety of the combined serotonin-dopamine antagonist risperidone in mentally retarded patients with persistent behavioural disturbances. After an observation period of 1 week, risperidone 4-12 mg or placebo was administered during 3 weeks as add-on treatment to the existing medication, followed by a 1-week single-blind placebo wash-out, and another 3 weeks of double-blind treatment with the cross-over medication. Thirty-seven patients participated in the trials; 30 completed the study.