Risperidone (pronounced Ris-PER-i-don and sold under the trade name Risperdal in the United States, Canada, the United Kingdom.

Risperidone (pronounced Ris-PER-i-don and sold under the trade name Risperdal in the United States, Canada, the United Kingdom, Portugal and several other countries, Risperdal or Ridal in New Zealand, Rispolept in Eastern Europe, and Belivon, or Rispen elsewhere) is an atypical antipsychotic medication developed by Janssen Pharmaceutica. It was approved by the United States Food and Drug Administration (FDA) in 1993 for the treatment of schizophrenia. On Wednesday, August 22, 2007, Risperdal was approved as the only drug agent available for treatment of schizophrenia in children ages 13–18; it was also approved that same day for treatment of bipolar disorder in youths ages 10–18, joining lithium. Risperidone contains the functional groups of benzisoxazole and piperidine as part of its molecular structure. In 2003 the FDA approved risperidone for the short-term treatment of the mixed and manic states associated with bipolar disorder. In 2006 the FDA approved risperidone for the treatment of irritability in children and adolescents with autism. Like other atypical antipsychotics, it has also been used "off-label" for the treatment of anxiety disorders, such as Obsessive-Compulsive disorder; severe, treatment-resistant depression with or without psychotic features; Tourette's disorder; disruptive behavior disorders in children; and eating disorders, among others.

Janssen's patent on Risperdal expired on December 29, 2007, opening the market for cheaper generic versions of the drug from other companies; however, Janssen will continue to have exclusive marketing rights until June 29, 2008, as the result of a pediatric extension.

Risperidone is available as a tablet in 0.25, 0.5, 1, 2, 3 and 4 mg sizes, and as a 25 mg, 37.5 mg and 50 mg ampoule Risperdal Consta, which is a depot injection administered once every two weeks. It is also available as a wafer known in the United States as Risperdal M-Tabs and elsewhere as Risperdal Quicklets.

Side effects
Common side effects include akathisia, anxiety, insomnia, low blood pressure, muscle stiffness, muscle pain, sedation, tremors, increased salivation, and stuffy nose. Risperidone has been associated with minimal to moderate weight gain, with one study finding that 26 to 38 percent of participants on the drug experienced weight gain.It has also been known to cause sexual dysfunction such as retrograde ejaculation.

Occasionally breast tenderness and eventually lactation in both genders may occur. Many antipsychotics are known to increase prolactin because they inhibit dopamine. However, risperidone is known to increase prolactin to a greater extent than most other antipsychotics, such as quetiapine. It is thought that once risperidone raises prolactin, it may cause non-cancerous tumors in the pituitary gland. This may recur even if the patient has switched to a different antipsychotic.

Risperidone can potentially cause tardive dyskinesia (TD), extrapyramidal symptoms (EPS), and neuroleptic malignant syndrome (NMS), although the risk is generally less than for the older typical antipsychotics.

Also, risperidone can trigger diabetes and more serious conditions of glucose metabolism, including ketoacidosis and hyperosmolar coma.

Pharmacology
Risperidone is a strong dopamine blocker (antagonist); i.e., it inhibits functioning of postsynaptic dopamine receptors.

It reaches peak plasma levels quickly regardless of whether it is administered as a liquid or pill. The strong dopamine-blocking reaction is known to make some people feel nauseated if they do things that normally trigger the dopamine response, such as eat a pleasing meal or experience orgasm[original research?][citation needed]. Risperidone is metabolised fairly quickly, so this potential for nausea subsides usually in two to three hours. However the active metabolite, 9-hydroxy-risperidone, which has similar pharmacodynamics to risperidone, lingers in the body for much longer.

An intramuscular preparation, marketed as Risperdal Consta, can be given once every two weeks. It is slowly released from the injection site. It can be useful in patients who have difficulty taking oral medication for any reason. Some people prefer a once-every-two-weeks injection to daily pills. It also helps the physician ensure compliance. Doses range from 25 to 50 mg given as an intramuscular injection once every two weeks.