Risperidone

Risperidone (Belivon®, Rispen®, Risperdal® in the United States) is an atypical antipsychotic medication. It was approved by the United States Food and Drug Administration (FDA) in 1993. It is most often used to treat delusional psychosis (including schizophrenia), but risperidone (like other atypical antipsychotics) is also used to treat some forms of bipolar disorder, psychotic depression and Tourette syndrome.

Generally lower doses are used for autistic spectrum disorders than are used for schizophrenia and other forms of psychosis; risperidone has received approval from the Food and Drug Administration (FDA) for symptomatic treatment of irritability in autistic children and adolescents.

Risperidone is now the most commonly prescribed antipsychotic medication in the United States.

Side effects

Common side effects include nausea, anxiety, dizziness, insomnia, low blood pressure, muscle stiffness, muscle pain, sedation, tremors, increased salivation and weight gain (it is not uncommon for patients taking risperidone over long periods to gain upwards of 50 pounds or even more). It has also been known to cause sexual dysfunction.

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 tumours in the pituitary gland. This may recur even if the patient has switched to a different antipsychotic.

Like all antipsychotics, 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.

For some personal reports of the effects of using risperidone for autism or Asperger's syndrome - occasionally beneficial especially at very low doses such as 0.5mg per day, but sometimes severely distressing even at low doses.

Pharmacology

Risperidone is a very strong dopamine blocker (antagonist); ie. it inhibits functioning of postsynaptic dopamine receptors.

Risperidone also acts as a 5-HT2A antagonist, and can be used to quickly and effectively block the effects of 5-HT2A agonist drugs such as LSD.

It reaches peak plasma levels quickly regardless of whether it is administered as a liquid or pills. 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. Risperidone is metabolised fairly quickly so this potential for nausea subsides usually in two to three hours.

Safety risks

In 2004, the Committee for the Safety of Medicines (CSM) in the UK issued a warning that risperidone and another atypical antipsychotic, olanzapine, should not be given to elderly patients with dementia, because of an increased risk of cerebrovascular adverse events including stroke.

A study in the June 2006 edition of the journal Pharmacotherapy has highlighted a possible link between risperidone and pituitary tumours. The study examined the FDA's Adverse Event Reporting System database and found 77 pituitary tumours associated with antipsychotics. Of these, risperidone was associated with 54 (70%). One co-author cautioned that "Our findings do not prove a causal relationship between antipsychotic medications and pituitary tumours" and "atypical antipsychotics are lifesaving medications for a lot of people. By no means are we advocating that people stop using them, especially risperidone".

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