Research Guide · Updated August 2026

Retatrutide vs Semaglutide: UK Research Comparison

Short answer: retatrutide shows the larger effect in published trials — 24.2% mean body-weight reduction at 48 weeks against semaglutide's 14.9% at 68 weeks — while semaglutide has the deeper safety and cardiovascular evidence base. Below we compare the two side by side on mechanism, trial data, weekly dosing and UK research supply, so you can pick the right vial for your protocol.

Mechanism

Semaglutide is a pure GLP-1 receptor agonist — the same class as liraglutide, refined for once-weekly dosing.

Retatrutide is a triple agonist at GLP-1, GIP and glucagon receptors. The glucagon component drives additional energy expenditure via hepatic and adipose signalling.

Published trial data

Semaglutide STEP-1 (NEJM 2021): 14.9% mean body-weight reduction at 68 weeks (2.4 mg weekly).

Retatrutide TRIUMPH-1 (NEJM 2023): 24.2% at 12 mg weekly at 48 weeks — the highest published effect size for any incretin to date.

Cardiovascular outcomes are proven for semaglutide (SELECT trial 2023); retatrutide is still in Phase 3 with cardiovascular outcome data pending.

Dosing intervals

Both are once-weekly candidates. Semaglutide has a half-life of ~7 days; retatrutide ~6 days. Titration schedules in both trial programmes escalated monthly to minimise GI adverse events.

Sourcing in the UK

Professor Peptide dispatches both peptides from the UK with tracked courier and a Certificate of Analysis (HPLC + mass spec) for every batch. Free tracked shipping on every order.

Frequently Asked Questions

Which produces more weight loss in trials — retatrutide or semaglutide?+

Retatrutide's Phase 2 data (24.2% at 48 weeks) exceeds semaglutide's Phase 3 data (14.9% at 68 weeks), but head-to-head trials have not yet been published.

Are both legal to buy in the UK?+

Yes, both are legal for laboratory research use. Neither may be sold or supplied for human consumption without an MHRA authorisation.

Do they require different storage?+

No — both are lyophilised, stored at 2–8 °C before reconstitution, and stable ~28 days refrigerated once reconstituted with bacteriostatic water.

Which vial size is best for a longer study?+

10 mg or 15 mg vials reduce the number of reconstitutions and freeze-thaw cycles required over a multi-week protocol.