• Engagement with FDA on GH001 IND complete response ongoing
• The fully completed Open-Label Extension analysis confirms a 73% remission rate at 6 months with infrequent treatment visits and no psychotherapy
• Treatment was well tolerated and no treatment related serious adverse events were reported. There was no evidence of treatment-emergent suicidal ideation or behavior
• Global pivotal program initiation on track for 2026

GH Research PLC (Nasdaq: GHRS), a clinical-stage biopharmaceutical company dedicated to transforming the lives of patients by developing a practice-changing treatment in depression, today provided updates on its business and key upcoming milestones.

GH001 Update

We have recently announced that we submitted a complete response to the previously announced clinical hold on our Investigational New Drug Application (IND) for GH001 with the U.S. Food and Drug Administration (FDA). We have now received a response from the FDA with only one hold topic remaining. The FDA requested that we either provide additional data or further justification related to the previously announced respiratory tract histology findings in rats. We strongly believe, based on scientific evidence, that the respiratory tract histology findings are rat specific. There are no additional requests related to dog toxicology. There are no device related issues remaining.

Engagement with FDA on IND complete response is ongoing. We are actively working to address the remaining issue.

Final Data from Fully Completed Phase 2b TRD

Previously we reported on the initial results from the phase 2b clinical trial of GH001 in treatment-resistant depression (TRD). This included part of the open-label extension (OLE) phase. Today we can report on the full dataset.

The primary endpoint was met with a highly significant placebo adjusted reduction from baseline of -15.5 points in Montgomery-Åsberg Depression Rating Scale (MADRS) total score on Day 8 (p<0.0001).

The full analysis of the OLE confirms a 73% remission rate at 6 months with infrequent treatment visits and no mandated psychotherapeutic intervention. GH001 delivered consistent MADRS reduction with re-treatments as needed. 57.5% of patients achieved remission at day 8 and 90% of those were also in remission at month 6.

Safety analysis confirmed that 100% of patients from the double-blind (DB) part continued in the OLE and there were no treatment related serious adverse events across the full 6-month duration of the trial. No treatment-emergent events of suicidal intent or suicidal behaviour occurred throughout the 6-month duration of the trial and lower rates of suicidal ideation were observed during the study in comparison to baseline. The psychoactive experience had a median duration of 11 minutes across the DB and OLE parts of the trial.

Across the DB and OLE, patients were deemed discharge ready by 1 hour from dose administration at 99% of treatment visits. A majority of patients needed 1-2 doses of GH001 suggesting a 2-hour visit or less in a commercial setting.

GH002 Update

We have previously announced the completion of a Phase 1, dose-ranging clinical pharmacology trial of GH002, our proprietary intravenous mebufotenin HBr product candidate, in healthy volunteers.

Top-line results demonstrate that GH002 was well-tolerated with no severe or serious adverse events and produced ultra-rapid psychoactive effects. The pharmacokinetic profile of GH002 was equivalent to that of GH001. We expect to submit an IND with the FDA for GH002 in Q4 2025.

Global Pivotal Program Plans

Pivotal program planning has been ongoing since Q1 2025:

• We have established a steering committee with KOLs to review Phase 2b results and assist with design of pivotal program;
• CRO and site selection process is ongoing and we are ramping up the team with laser focus on execution; and
• We are in the process of getting regulatory input on phase 3 requirements and preparation for end-of-phase 2 meeting is underway.

On that basis, we expect to initiate our global pivotal program in 2026.