Tirzepatide vs retatrutide (UK): what the head-to-head data suggests

UK researchers frequently ask how tirzepatide (Mounjaro / Zepbound) compares to retatrutide. There is no direct head-to-head trial. What we have is cross-trial data: SURMOUNT-1 reported ~20.9% mean weight reduction with tirzepatide 15 mg at 72 weeks; retatrutide Phase 2 (Jastreboff, 2023) reported ~24.2% at just 48 weeks with 12 mg.

Mechanistically, tirzepatide is a dual GIP/GLP-1 agonist. Retatrutide adds glucagon-receptor activity, which is thought to drive additional energy expenditure and hepatic-fat loss — at the cost of a modest heart-rate signal. Full head-to-head comparison lives in the semaglutide vs tirzepatide and retatrutide vs tirzepatide pages.

Practical UK note: tirzepatide is MHRA-licensed as Mounjaro. Retatrutide is investigational only. Pricing and pen-format questions for retatrutide are covered in the retatrutide pen price guide.