Pimavanserin (ACP-103) is a selective inverse agonist of the 5-hydroxytryptamine 
2A (5-HT2A) receptor intended to treat patients with Parkinson's disease 
psychosis (PDP). Currently there are no FDA-approved medications in the United 
States for the treatment of PDP, although on September 2, 2014, the United 
States Food and Drug Administration granted breakthrough therapy status to 
pimavanserin, highlighting the unmet need for therapeutics in this class. Most 
antipsychotic medications worsen motor dysfunction due to dopamine antagonism, 
and all carry a black box warning for an increased risk of mortality in elderly 
patients with dementia-related psychosis. Data from phase II and phase III 
clinical trials suggest that pimavanserin is a safe and effective treatment 
option for PDP. Trial results indicate a significant reduction in hallucinations 
and delusions in patients with PDP without worsening motor symptoms. Additional 
studies are ongoing for the treatment of Alzheimer's psychosis, schizophrenia 
and insomnia. Such promising outcomes warrant a review of the available 
literature regarding pimavanserin and its use in the treatment of PDP symptoms.