Navacaprant's failure to separate from placebo in two consecutive Phase III trials closes the door on kappa opioid receptor antagonism as a near-term treatment approach for major depressive disorder, and forces Massachusetts-based Neumora Therapeutics (Nasdaq: NMRA) into a full strategic reset with a pipeline that has yet to generate Phase III-ready data.
Neumora reported that navacaprant 80 mg failed to achieve statistical significance on the primary endpoint in both the KOASTAL-2 and KOASTAL-3 studies. In KOASTAL-2, the least-squares mean difference versus placebo was -0.3 points on the Montgomery-Åsberg Depression Rating Scale at week 6 (p=0.813). In KOASTAL-3, the drug performed numerically worse than placebo, with a difference of +0.7 points (p=0.480). A pre-specified analysis of 426 patients enrolled after protocol optimizations in early 2025 produced a least-squares mean difference of 0.0 (p=0.976). The results are unambiguously negative across every population examined.
The magnitude of the placebo response — a change from baseline of roughly 12 points in KOASTAL-2 — is consistent with a long-standing challenge in MDD trials, where site and patient selection variability can obscure even genuine drug effects. Neumora had introduced study optimizations in early 2025 specifically to address this issue, making the near-zero treatment effect in the optimized cohort particularly difficult to interpret as anything other than a signal of insufficient efficacy.
A program with a contested foundation
The failure is not entirely surprising in context. Securities class action litigation filed against Neumora in early 2025 alleged that the company had been forced to modify the original Phase II inclusion criteria — developed under predecessor company BlackThorn Therapeutics — to show a statistically significant signal in moderate-to-severe MDD patients, and that the Phase II dataset lacked the statistical power to reliably predict Phase III outcomes. The KOASTAL program enrolled over 850 patients across two adequately powered trials, leaving little room to attribute the null result to chance.
Navacaprant is designed to block the kappa opioid receptor, a target implicated in the regulation of mood, stress response, and anhedonia. The hypothesis that KOR antagonism could produce antidepressant effects was scientifically plausible and supported by preclinical evidence, but the clinical validation never materialized. No approved therapy targets this mechanism in MDD, and the KOASTAL failures will likely dampen enthusiasm for the approach across the industry, at least in the near term.