Risperidone, sold under the brand name Risperdal among others, is an atypical antipsychotic. It is used to treat schizophrenia, bipolar disorder, and irritability associated with autism. It is taken either by mouth or by injection into a muscle. The injectable version is long-acting and lasts for about two weeks.
Common side effects include movement problems, sleepiness, dizziness, trouble seeing, constipation, and increased weight. Serious side effects may include the potentially permanent movement disorder tardive dyskinesia, as well as neuroleptic malignant syndrome, an increased risk of suicide, and high blood sugar levels. In older people with psychosis as a result of dementia, it may increase the risk of dying. It is unknown if it is safe for use in pregnancy. Its mechanism of action is not entirely clear, but is believed to be related to its action as a dopamine antagonist and serotonin antagonist.
Study of risperidone began in the late 1980s and it was approved for sale in the United States in 1993. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2017, it was the 156th most commonly prescribed medication in the United States, with more than four million prescriptions.