Background: Up to 15% of patients with major depressive disorder (MDD) attempt suicide and up to 2% complete suicide. This was a post-hoc analysis aimed to evaluate the risk of suicide ideation and behavior associated with adjunctive pimavanserin treatment in adults with MDD. Methods: CLARITY was a randomized, double-blind, placebo-controlled study in patients with MDD and an inadequate response to a selective serotonin reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI). For this post-hoc analysis, the primary endpoint was mean change from baseline for HAMD item 3 (suicide). The incidence of suicidal ideation or behavior was also assessed from the Columbia-Suicide Severity Rating Scale (C-SSRS) and reports of adverse events. Results: During Stage 1, LS mean change for HAMD Item 3 was reduced from baseline at each week with pimavanserin with a significant difference between pimavanserin and placebo at Week 3 (p=0.012, effect size: 0.431). At any post-baseline assessment, suicidal ideation on the C-SSRS was reported in 28 (18.1%) of patients with placebo and 9 (17.3%) with pimavanserin during Stage 1 and in 7 (20.7%) with placebo and 4 (13.8%) with pimavanserin during Stage 2. No events of suicidal behavior were observed with either placebo or pimavanserin. Limitations: : The post hoc nature, exclusion of patients with any history of suicide from the primary study, and the small number of patients who demonstrated evidence of suicidal ideation. Conclusions: Adjunctive pimavanserin was not associated with an increase in suicidal ideation in patients with MDD. Further study is needed to verify these results.