OBJECTIVE: Our aim was to describe the efficacy and tolerability of 
pimavanserin, a highly selective serotonin 5-HT2A receptor inverse 
agonist/antagonist indicated for the treatment of hallucinations and delusions 
associated with Parkinson's disease psychosis (PDP), using the metrics of number 
needed to treat (NNT) and number needed to harm (NNH).
METHODS: Categorical efficacy and tolerability data were extracted from the 
clinical trial databases of the double-blind placebo-controlled studies of 
pimavanserin in persons with PDP. NNT and NNH values were calculated with their 
respective 95% confidence intervals. The likelihood to be helped or harmed (LHH) 
was then calculated contrasting therapeutic response versus discontinuation 
because of an adverse event.
RESULTS: NNT values for pimavanserin 34 mg/d versus placebo for several 
definitions of clinical response are 10, and/or are not statistically 
significant, and/or show an advantage for pimavanserin over placebo (such as for 
postural hypotension). In terms of LHH, pimavanserin 34 mg/d is about five times 
more likely to result in clinical response (as measured by a ≥3 point decrease 
from baseline on the Scale for the Assessment of Positive Symptoms adapted for 
Parkinson's disease) versus discontinuation due to an adverse event.
CONCLUSIONS: Using the metrics of NNT, NNH, and LHH, pimavanserin 34 mg/d for 
the treatment of PDP appears to have a compelling benefit/risk profile.