Encyclopedia entry
Retatrutide (UK): triple-agonist GLP-1/GIP/glucagon under investigation
Oliver Mackman · Editorial director · Best Business Loans Ltd (16833937)
Last updated 2026-05-20
Retatrutide is a synthetic peptide developed by Eli Lilly and Company that targets three receptors simultaneously: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. It is classified as a triple-agonist or "triagonist" compound. As of May 2026, Retatrutide is in phase III clinical trials under Eli Lilly's TRIUMPH programme and has not been approved or licensed by the MHRA, FDA, or any regulatory authority. It cannot be prescribed in the UK. It cannot be supplied by UK pharmacies. Research-peptide retailers in the UK sell it under "research use only, not for human or animal consumption" framing. PeptideClear publishes encyclopedia commentary only and does not recommend human use.
What it is
Retatrutide (also known by the research identifier LY3437943) is a long-acting injectable peptide. Its triple-receptor mechanism distinguishes it from licensed dual-agonists such as tirzepatide (GLP-1/GIP only). The simultaneous glucagon receptor action is hypothesised in clinical literature to drive additional metabolic effects, particularly on energy expenditure, compared with dual-agonist compounds.
- · Developer: Eli Lilly and Company (Indianapolis, USA).
- · Mechanism: simultaneous agonism at GLP-1R, GIPR, and glucagon receptor.
- · Format: once-weekly subcutaneous injection in clinical trial settings.
- · Status: phase III clinical development (TRIUMPH programme). No regulatory approval in any country as of May 2026.
Clinical development status
Retatrutide phase II results were published in the New England Journal of Medicine in 2023. According to published clinical trial data, participants receiving Retatrutide across the 48-week phase II period showed substantial reductions in body weight, with some cohorts in the trial achieving results that the authors described as the highest reported in a phase II study of any obesity treatment to that point. PeptideClear does not republish specific efficacy figures as recommendations. Readers should consult the original NEJM publication (Jastreboff et al., NEJM, July 2023) for the reported data.
- · Phase II: results published NEJM July 2023. 48-week duration. Multiple dose cohorts.
- · Phase III: TRIUMPH programme, ongoing. Results not yet published as of May 2026.
- · Independent academic literature: limited. Phase III data will form the primary evidence base for any future regulatory submission.
- · No head-to-head data against tirzepatide or semaglutide published in peer-reviewed literature as of May 2026.
All claims above are sourced from published peer-reviewed clinical trial data. PeptideClear does not extrapolate from trial data to individual outcomes.
UK regulatory framing
Important: not licensed for use in the UK
Retatrutide is not currently licensed by the MHRA or any other regulator. It is not a prescribable medicine in the UK. It cannot be supplied by any UK pharmacy. It is not the same as Mounjaro (tirzepatide) or Wegovy (semaglutide), which are MHRA-licensed medicines available via UK prescribers. Do not use any Retatrutide product without consultation with a UK-licensed prescriber. Research-tier supply does not substitute for a licensed medical product.
- · Not a controlled drug under the Misuse of Drugs Act 1971.
- · Not scheduled under the Psychoactive Substances Act 2016.
- · No UK marketing authorisation as a medicine. Phase III trials are ongoing; regulatory submission has not occurred.
- · Sold legally as a research chemical when marketed without health or therapeutic claims.
- · Becomes an unlicensed medicinal product the moment a retailer or commentator makes therapeutic claims about it.
- · The supply chain for research-tier Retatrutide is distinct from Eli Lilly's clinical trial supply. Purity, source, and authenticity cannot be verified by the buyer through any public mechanism.
Adjacent compounds under investigation
Retatrutide is one of several next-generation compounds under active clinical investigation in the metabolic and obesity space. Two adjacent compounds researchers may encounter in the same context:
- · Cagrilintide: a long-acting amylin analogue developed by Novo Nordisk. In combination trials with semaglutide (CagriSema). Mechanism differs from GLP-1 agonism: targets amylin receptors involved in satiety signalling.
- · Mazdutide: a dual GLP-1/glucagon receptor agonist (no GIP component) developed by Innovent Biologics. Phase II data published for metabolic endpoints. Not approved in the UK.
All three compounds are unlicensed in the UK as of May 2026 and are available only through research-peptide retailers under research-use-only framing.
Supply quality: why CoA practice matters more here
For well-characterised research peptides such as BPC-157 or TB-500, multiple UK retailers have years of customer feedback and established supply relationships. For Retatrutide, the compound is more complex to synthesise correctly, the phase III trial data has not yet been published, and no pharmaceutical-grade UK supply exists outside of clinical trials.
Unlike Mounjaro or Wegovy, which are supplied by Eli Lilly and Novo Nordisk respectively through regulated UK pharmacy channels, any Retatrutide sold by research-peptide retailers is not connected to Eli Lilly's manufacturing or quality-control process. The compound in a research vial is produced by third-party peptide synthesis facilities.
- · CoA (Certificate of Analysis) practice is the only public quality signal available. Retailers who publish CoAs via open subdomains or verifiable QR codes provide more accountability than those who gate CoAs behind email requests or do not publish them at all.
- · Named lab partners provide more recourse than unnamed "third-party" claims.
- · Our UK retailers comparison ranks research peptide retailers on CoA transparency, trading tenure, and corporate identity.
UK retailers stocking Retatrutide
A small number of UK research-peptide retailers stock Retatrutide. PeptideClear compares them on CoA transparency, trading tenure, and operator identity. Research use only.
Compare UK retailersPopular on PeptideClear
Ready to buy
Buy RETATRUTIDE in the UK
UK retailers compared by price, Trust Index, and CoA practice. Editorial commentary only. Research use only.