Risperidone

Risperidone, sold under the brand name Risperdal among others, is an atypical antipsychotic used to treat schizophrenia and bipolar disorder, as well as aggressive and self-injurious behaviors associated with autism spectrum disorder. It is taken either by mouth or by injection (i.e., subcutaneous or intramuscular). The injectable versions are long-acting and last for 2–4 weeks.

Common side effects include weight gain, drowsiness, fatigue, insomnia, dry mouth, constipation, elevated prolactin levels, and restlessness. 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 death. 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 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 2022, it was the 183rd most commonly prescribed medication in the United States, with more than 2 million prescriptions.