Zuranolone Shows Consistent Effects Across Japanese Depression Subgroups

A pooled analysis of two randomized, double-blind, placebo-controlled trials found that zuranolone produced consistent treatment effects among Japanese patients with major depressive disorder, including across groups defined by baseline severity, sex, episode recurrence and other baseline characteristics. The study pooled 562 participants from a Phase 2 trial and a Phase 3 trial: 284 received oral zuranolone and 278 received placebo once daily for 14 days. Patients were then followed for six weeks. The main efficacy measure was the change from baseline in the 17-item Hamilton Rating Scale for Depression, known as HAM-D17.

During the 14-day treatment period, zuranolone reduced symptoms across three components of the HAM-D17: core depression, anxiety and insomnia. The insomnia subscale accounted for the largest part of the difference between zuranolone and placebo in the overall HAM-D17 total score. This does not mean that insomnia was the only symptom domain affected, because reductions were also observed in the core and anxiety subscales. Rather, the pooled comparison indicated that differences in sleep-related symptoms contributed most strongly to the overall treatment separation measured during active treatment.

The symptom domains followed different patterns after treatment ended. Reductions in insomnia scores tended to lessen during the six-week follow-up, while improvements in the core depression and anxiety subscales were relatively maintained. These descriptive trajectories accompanied the broader pattern reported for the HAM-D17 total score: improvement was evident as early as Day 3 and remained after the treatment period. The analysis therefore suggests that the timing and persistence of individual symptom changes varied within the overall antidepressant response.

The investigators also examined response and remission rates alongside changes in the HAM-D17 total score and its subscales. Subgroup analyses showed that the treatment effect of zuranolone did not materially differ according to baseline severity, sex, recurrence history or other examined characteristics. The findings indicate a broadly consistent treatment effect in the population studied, rather than evidence that one demographic or clinical subgroup accounted for the pooled result. Because the analysis was conducted after the underlying trials, its subgroup and symptom-domain results should be interpreted as exploratory.

The work has important limits. The analysis combined data from separate Phase 2 and Phase 3 placebo-controlled trials in Japanese patients, and it was not designed as a new randomized comparison. Subscale findings describe how the difference between treatment groups was distributed across symptoms; they do not establish that insomnia or anxiety independently caused the overall reduction in depression scores. The maintenance of core and anxiety improvements is likewise an observed temporal pattern, not proof of a durable mechanism. The authors state that hypothesis-driven studies are needed to confirm these exploratory findings. As a result, the results support the consistency of the measured zuranolone effect across the analyzed subgroups while leaving the clinical interpretation of symptom-specific trajectories for future research.

Subject of Research: Exploratory pooled analysis of zuranolone efficacy across subgroups and symptom domains in Japanese patients with major depressive disorder.

Article Title: Characterizing the efficacy of zuranolone across patient subgroups and symptom domains in Japanese patients with major depressive disorder: a pooled analysis of two placebo-controlled trials

Article References: Kato, M., Baba, T., Sonoyama, T., & Iwata, N. (2026). Characterizing the efficacy of zuranolone across patient subgroups and symptom domains in Japanese patients with major depressive disorder: a pooled analysis of two placebo-controlled trials. Frontiers in Psychiatry, 17, Article 1891881. https://doi.org/10.3389/fpsyt.2026.1891881

Image Credits: AI Generated

DOI: 10.3389/fpsyt.2026.1891881

Keywords: zuranolone, major depressive disorder, Japanese patients, pooled analysis, HAM-D17, insomnia, anxiety, core depression, antidepressant response, post hoc analysis, Characterizing, efficacy