The present invention relates to a risperidone sustained release delivery system for treatment of medical conditions relating to delusional psychosis, schizophrenia, bipolar disorder, psychotic depression, obsessive-compulsion disorder, Tourette syndrome, and autistic spectrum disorders. The sustained release delivery system includes a flowable composition containing risperidone, a metabolite, or a prodrug thereof and an implant containing risperidone, a metabolite, or a prodrug thereof. The flowable composition may be infected into tissue whereupon it coagulates to become a solid or gel, monolithic implant. The flowable composition includes a biodegradable, thermoplastic polymer, an organic liquid, and risperidone, a metabolite or a prodrug thereof.