The clinical development of Retatrutide is one of the most closely watched programmes in metabolic research. This article covers the full trial history, the landmark Phase 2 data, and what Phase 3 means for Retatrutide in the UK in 2026.

Phase 1: First-in-Human Safety Data

Initial Phase 1 studies established the safety, tolerability and pharmacokinetic profile of Retatrutide across dose levels from sub-therapeutic to active ranges. The compound demonstrated a half-life consistent with weekly dosing — a key practical advantage for structured research protocols.

Phase 2: The NEJM-Published Landmark Data

The pivotal Phase 2 trial enrolled 338 adults with obesity (BMI ≥27) across multiple international sites. Published in the New England Journal of Medicine in 2023, it was a randomised, double-blind, placebo-controlled study evaluating Retatrutide weekly doses from 1mg to 12mg over 48 weeks.

Primary Outcomes

• 22.5% mean body weight reduction at highest dose (12mg)
• 18.3kg mean weight loss over 48 weeks
• Significant reductions in HbA1c, fasting blood glucose, systolic blood pressure and triglycerides
• Meaningful waist circumference reduction across all dose levels

“Retatrutide produced substantially greater weight loss than has been observed with any previously approved antiobesity medication.” — NEJM 2023

Phase 3: Status in 2026

Phase 3 trials — assessing Retatrutide efficacy and safety in larger, more diverse populations — are actively underway globally, including in the UK. The SURMOUNT-like Phase 3 programme is expected to confirm Phase 2 findings at scale and provide the regulatory submission package for MHRA and FDA review.

Join Retatrutide Clinical Trials UK

The NIHR Be Part of Research database lists all UK-available trials including Retatrutide Phase 3 sites. Participation involves receiving the compound under full clinical supervision as part of a formally approved programme.

Retatrutide for R&D Researchers in 2026

While Phase 3 proceeds toward regulatory submission, Retatrutide UK is available as an R&D compound for qualified researchers. Alluvi Healthcare stocks the Alluvi Retatrutide 20mg and 40mg pens for research use only — clearly labelled and batch-tested. This is not a clinical trial and these products are not medicines.