<p>The mechanism of action of pimavanserin in the treatment of hallucinations and delusions associated with Parkinson&#39;s disease psychosis is unknown. However, the effect of pimavanserin could be mediated through a combination of inverse agonist and antagonist activity at serotonin 5-HT 2A receptors and to a lesser extent at serotonin 5-HT2C&nbsp;receptors.</p>