AtaiBeckley's BPL-003 Shows Rapid, Durable TRD Response on SSRIs

On 8 April 2026, AtaiBeckley Inc. announced peer-reviewed Phase 2a results for BPL-003 (mebufotenin benzoate), a 5-HT1A and 5-HT2A agonist, published in CNS Drugs. The open-label study evaluated a single intranasal dose in 12 adults with treatment-resistant depression (TRD) who remained on stable selective serotonin reuptake inhibitor (SSRI) therapy throughout. Both the 10 mg and 12 mg cohorts achieved a 66.7% antidepressant response rate, defined as a ≥50% reduction from baseline Montgomery-Asberg Depression Rating Scale (MADRS) score, by Day 2, with 83% of responders in the 10 mg cohort maintaining response at Day 85.

Mechanism

BPL-003 is a proprietary intranasal formulation of mebufotenin benzoate. Its dual agonism at 5-HT1A and 5-HT2A receptors is mechanistically distinct from SSRIs, which act through reuptake inhibition rather than direct receptor engagement; this difference may account for the speed of onset observed in this cohort. The treatment session lasts approximately two hours; mean discharge readiness was 102 minutes post-dose in the 10 mg cohort and 96 minutes in the 12 mg cohort. Transient blood pressure elevations occurred following dosing in both cohorts, peaking at 10 minutes post-dose and returning to baseline by 90 minutes, with no accompanying cardiovascular symptoms.

Evidence

The publication reports Part 2 of a four-part Phase 2a programme under NCT05660642, specifically the SSRI-concomitant cohort. The Part 2 study enrolled 12 adults with moderate-to-severe TRD, baseline MADRS score ≥24, who had failed at least two prior antidepressants and continued on stable SSRI therapy throughout. A single intranasal dose achieved a 66.7% response rate by Day 2 in both cohorts. Durability at Day 85 was 83% (5 of 6 participants) in the 10 mg cohort and 66.7% (4 of 6) in the 12 mg cohort. No serious adverse events were reported in the Part 2 cohort.

Commercial and Programme Context

BPL-003 received FDA Breakthrough Therapy Designation in October 2025, following End-of-Phase 2 alignment that has placed Phase 3 initiation on track for Q2 2026. The design of the Part 2 study, in which BPL-003 was administered on top of stable SSRI therapy rather than in place of it, reflects a positioning logic that is different to existing rapid-acting options. Esketamine, also approved for TRD, requires in-office administration under medical supervision with a mandatory post-dose observation period. A drug that works alongside existing oral antidepressant therapy, with a roughly 100-minute session window, represents a different clinical workflow and entry point.

What This Means

Esketamine demonstrated sustained improvement in MADRS scores during open-label treatment with reduced dosing frequency in a 2018 study by Daly et al. in JAMA Psychiatry. BPL-003's Day 2 response rate and 10 mg cohort durability data are consistent with a rapid-onset profile, but direct comparison with esketamine is constrained by differences in study design, patient population, and the metrics each trial reported.

The claim-integrity boundary is meaningful. The Part 2 study is open-label; the sample is 12 participants; and there is no placebo arm, so the magnitude of effect attributable to BPL-003 beyond continued SSRI therapy alone cannot be separated from this data. Durability at Day 85 in the 10 mg cohort is an observation from six participants. Phase 3 is the appropriate frame for drawing efficacy conclusions, as opposed to a validation exercise.

Phase 3 initiation in Q2 2026, on the back of a Breakthrough Therapy Designation, places BPL-003 on an accelerated regulatory trajectory for a drug class that the FDA has shown it is prepared to move on. Whether the Phase 3 design preserves the SSRI co-administration model will determine if BPL-003 reaches the market as an adjunctive treatment or as a standalone option; a distinction that affects commercial positioning.

Sources

1. AtaiBeckley Inc. AtaiBeckley's BPL-003 Shows Rapid, Durable Antidepressant Response in Treatment-Resistant Depression Patients on SSRIs; Phase 2a Data Published in CNS Drugs. GlobeNewswire, 8 April 2026.
2. Seynaeve M, et al. Intranasal 5-MeO-DMT Concomitant with SSRI for Treatment-Resistant Depression: A Proof-of-Concept Trial. CNS Drugs. 2026. 10.1007/s40263-025-01250-z.
3. Daly EJ, et al. Efficacy and Safety of Intranasal Esketamine Adjunctive to Oral Antidepressant Therapy in Treatment-Resistant Depression. JAMA Psychiatry. 2018;75(2):139–148. 10.1001/jamapsychiatry.2017.3739

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