Pimavanserin is a drug

Drug

A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 developed by Acadia Pharmaceuticals

Acadia Pharmaceuticals

ACADIA Pharmaceuticals, Inc. is a biopharmaceutical company. The company has a portfolio of four product candidates, including pimavanserin, which is in Phase III clinical development as a treatment for Parkinson's disease psychosis...

 which acts as an inverse agonist

Inverse agonist

In the field of pharmacology, an inverse agonist is an agent that binds to the same receptor as an agonist but induces a pharmacological response opposite to that agonist....

 on the serotonin receptor subtype 5-HT_2A

5-HT2A receptor

The mammalian 5-HT2A receptor is a subtype of the 5-HT2 receptor that belongs to the serotonin receptor family and is a G protein-coupled receptor . This is the main excitatory receptor subtype among the GPCRs for serotonin , although 5-HT2A may also have an inhibitory effect on certain areas such...

, with 10x selectivity over 5-HT_2C

5-HT2C receptor

The 5-HT2C receptor is a subtype of 5-HT receptor that binds the endogenous neurotransmitter serotonin . It is a G protein-coupled receptor that is coupled to Gq/G11 and mediates excitatory neurotransmission. HTR2C denotes the human gene encoding for the receptor, that in humans is located at the...

, and no significant affinity or activity at 5-HT_2B

5-HT2B receptor

5-hydroxytryptamine receptor 2B, also known as HTR2B, is a 5-HT2 receptor, but also denotes the human gene encoding it.-Function:...

 or dopamine receptor

Dopamine receptor

Dopamine receptors are a class of metabotropic G protein-coupled receptors that are prominent in the vertebrate central nervous system . The neurotransmitter dopamine is the primary endogenous ligand for dopamine receptors....

s. As of September 3 2009, pimavanserin has not met expectations for Phase III clinical trials for the treatment of Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

 psychosis

Psychosis

Psychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...

, and is in Phase II trials for adjunctive treatment of schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

 alongside an antipsychotic

Antipsychotic

An antipsychotic is a tranquilizing psychiatric medication primarily used to manage psychosis , particularly in schizophrenia and bipolar disorder. A first generation of antipsychotics, known as typical antipsychotics, was discovered in the 1950s...

medication. It is expected to improve the effectiveness and side effect profile of antipsychotics.