# What is retatrutide? Mechanism, development history and how it differs from existing medicines

> Retatrutide (LY3437943) is a once-weekly injectable triple agonist of GIP, GLP-1 and glucagon receptors, in development at Eli Lilly for obesity and related conditions.

Canonical: https://yezz.co.uk/what-is-retatrutide · Last reviewed: 2026-09-11 · Author: Nick Johnson, Independent Prescription Pricing Analyst, Medstack Ltd

## Key facts
- A once-weekly injection activating GIP, GLP-1 and glucagon receptors — the first “triple G” agonist to reach Phase 3.
- Wegovy mimics GLP-1 alone; Mounjaro mimics GIP + GLP-1; retatrutide adds glucagon receptor activity, proposed to increase energy expenditure and liver-fat burning.
- Phase 2 (NEJM, 2023): up to 24.2% average weight loss at 48 weeks on the highest dose.
- Phase 3 maintenance doses studied: 4 mg, 8 mg and 12 mg weekly, titrated from a low starting dose.
- Developed for obesity, overweight with related conditions and type 2 diabetes — and not approved for use anywhere, including the UK.

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Cite as: Nick Johnson. "What is retatrutide? Mechanism, development history and how it differs from existing medicines". Yezz, 2026-09-11. https://yezz.co.uk/what-is-retatrutide