What Is Retatrutide? UK Guide to the New Triple‑Agonist Weight Loss Drug

What Is Retatrutide?

Retatrutide (also known as LY‑3437943) is a novel “triple agonist” peptide under development by Eli Lilly targeting GLP‑1, GIP, and glucagon receptors, combining appetite suppression, increased insulin sensitivity, and elevated metabolic rate

How Does Retatrutide Work?

Unlike semaglutide or tirzepatide, which target one or two receptors, retatrutide’s multi-receptor action allows for enhanced fat‑burning, stronger appetite control, and improved glycaemic regulation—all in a once‑weekly injection.

Clinical Trial Results

In a Phase 2 study of 338 obese adults, participants on the 12 mg weekly dose lost an average of 24.2% of body weight over 48 weeks. Nearly two-thirds lost 20% or more, and many continued shedding weight beyond week 48 The Sun+6New England Journal of Medicine+6Diabetes.co.uk+6. Additional improvements included reductions in liver fat, triglycerides, and LDL cholesterol levels New England Journal of Medicine+10Reuters+10Verywell Health+10.

UK Availability & Regulatory Status

Retatrutide is currently in Phase 3 clinical trials, including sites in the UK. It has not yet been approved by the MHRA or NHS and is therefore not available through prescription or private clinics Reddit+15Reddit+15Oxford Online Pharmacy+15. Public availability in the UK is unlikely before 2026–2027, pending trial completion, MHRA review, and NICE/SCM approvals The Care Pharmacy.

Potential Side Effects

Reported side effects mirror those seen with other GLP‑1 agonists:

• Nausea, diarrhoea, vomiting, constipation
  Some trial participants experienced accelerated weight loss leading to fatigue, kidney stone risk, or bone issues—emphasizing the need for careful dosing and medical supervision New England Journal of Medicine+7Diabetes.co.uk+7Reddit+7The Care Pharmacy+1.

How It Compares to Other Drugs

Compared to semaglutide (marketed as Wegovy/Ozempic) and tirzepatide (Mounjaro), retatrutide shows superior weight-loss efficacy in trials. For context:

• Semaglutide: ~15 % loss over ~68 weeks

• Tirzepatide: up to ~22.5 % over 72 weeks

• Retatrutide: ~24 % in just 48 weeks Reddit+15The Times+15Diabetes.co.uk+15Reddit+1

What’s Next & Timeline

Phase 3 data is expected in 2025, earlier than initially planned. If outcomes remain positive, retatrutide could receive MHRA clearance within 2–3 years, followed by private prescription availability and potential NHS rollout after NICE review RedditThe Times.