Psychiatric treatment of persons with severe, recurring, or chronic disorders of mood, cognition, or behavior is increasingly provided in ambulatory settings where control of treatment shifts to the patient. Medicines are a fundamental component in the effective, comprehensive care of such severely ill patients, and often are required for prolonged periods. The author discusses ways to enhance the effectiveness and safety of medication usage, including objective evaluation of responses, awareness of predictable pharmacological factors, use of adequate but simplified regimens, recognition of the patient as a consumer of services, and appreciation of individual and interpersonal psychological factors. The author concludes that sound clinical judgement and common sense, as well as sensitivity to the needs, circumstances, and reactions of individual patients, can increase adherence to and success of any psychiatric treatment.