Retatrutide: evidence, half-life, and how to track it

By Tessaro Pty Ltd, the maker of Pepti · Last reviewed October 2026

This page is a reference, not a protocol. It sets out what the published trials actually report, what the compound's half-life means for a weekly record, and what a clean log holds. It contains no dose figures and no schedule, and the section further down explains why that is deliberate rather than an omission.

Reference

What trials report

Published data describe a mean body-weight reduction of 24.2 percent at 48 weeks in the Phase 2 trial, and report that 100 percent of participants in the two highest dose groups reached a reduction of at least 5 percent (Jastreboff et al., NEJM 2023). That first figure is the reason the compound drew the attention it did.

The sponsor announced Phase 3 topline results in stages: TRIUMPH-4, in adults with obesity and knee osteoarthritis, in December 2025; TRIUMPH-1 in May 2026; and TRIUMPH-2 and TRIUMPH-3, the latter in adults with severe obesity and established cardiovascular disease, in July 2026 (Eli Lilly, 2025–2026). Those were company announcements. Peer-reviewed Phase 3 papers began to appear in June 2026, and the figures below come from them; they are reported on a treatment-regimen basis, so they can differ from the topline figures. Detailed TRIUMPH-4 results had not appeared in PubMed when we checked in October 2026.

In adults with obesity without diabetes, TRIUMPH-1 reports a mean body-weight reduction of 25.0 percent at 80 weeks in the highest-dose group, against 3.9 percent with placebo, with less knee pain in participants with knee osteoarthritis and fewer apnoea-hypopnoea events in those with obstructive sleep apnoea (Jastreboff et al., NEJM 2026). In adults with obesity and type 2 diabetes, TRIUMPH-2 reports corresponding figures of 18.8 percent and 5.1 percent at 80 weeks; gastrointestinal events were the most common adverse events, and low blood pressure and dysesthesia were reported more often than with placebo (Bellido et al., Lancet 2026). In type 2 diabetes not controlled by diet and exercise alone, the 40-week TRANSCEND-T2D-1 trial reports greater reductions in HbA1c and body weight than with placebo (Bajaj et al., Lancet 2026).

Trials report 14.9 percent mean body-weight reduction at 68 weeks for semaglutide (Wilding et al., NEJM 2021), and 20.9 percent at 72 weeks for tirzepatide (Jastreboff et al., NEJM 2022). Those two figures are the context that makes the retatrutide figures legible — without them, a percentage is a number without a scale.

The comparison has real limits and they are worth stating plainly. These are three separate trials, run in different populations, over different durations, with different designs and endpoints. Lining the percentages up in a row is a convenience, not a head-to-head result, and no published trial has compared these agents directly at the time of writing. Published data also describe adverse effects concentrated in the gastrointestinal system. Phase 3 results have been announced and have begun to publish, and the sponsor has said it plans to submit a Biologics License Application to the US FDA in the first quarter of 2027 (Eli Lilly, July 2026). A submission is not an approval: no regulator has approved retatrutide, and further Phase 3 studies remain listed as ongoing.

Sources (11)

1. Jastreboff et al., New England Journal of Medicine, 2023 — retatrutide Phase 2 trial; the abstract reports a 24.2% body-weight reduction at week 48 (highest-dose group). PubMed 37366315
2. Wilding et al., New England Journal of Medicine, 2021 — semaglutide (STEP 1 trial); the abstract reports a mean 14.9% body-weight reduction at week 68. PubMed 33567185
3. Jastreboff et al., New England Journal of Medicine, 2022 — tirzepatide (SURMOUNT-1); the abstract reports a 20.9% body-weight reduction at week 72 (highest-dose group). PubMed 35658024
4. Urva et al., Lancet, 2022 — LY3437943 (retatrutide) phase 1b multiple-ascending-dose trial; the abstract reports a dose-proportional half-life of approximately 6 days. PubMed 36354040
5. Jastreboff et al., New England Journal of Medicine, 2026 — retatrutide Phase 3 trial in obesity without diabetes (TRIUMPH-1); the abstract reports a 25.0% body-weight reduction at week 80 in the highest-dose group versus 3.9% with placebo. PubMed 42814954
6. Bellido et al., Lancet, 2026 — retatrutide Phase 3 trial in obesity with type 2 diabetes (TRIUMPH-2); the abstract reports an 18.8% body-weight reduction at week 80 in the highest-dose group versus 5.1% with placebo, and more frequent hypotension and dysesthesia than with placebo. PubMed 42810372
7. Bajaj et al., Lancet, 2026 — retatrutide Phase 3 trial in type 2 diabetes (TRANSCEND-T2D-1); the abstract reports greater reductions in HbA1c and body weight than with placebo at week 40. PubMed 42250575
8. ClinicalTrials.gov, NCT07629401 — pre-approval, single-patient expanded access of retatrutide, sponsor Eli Lilly; first posted 5 June 2026, status available. View the trial record
9. Eli Lilly and Company, press release, 11 December 2025 — topline results from the Phase 3 TRIUMPH-4 trial in adults with obesity and knee osteoarthritis (company announcement, not a peer-reviewed paper). Read on lilly.com
10. Eli Lilly and Company, press release, 21 May 2026 — topline results from the Phase 3 TRIUMPH-1 trial (company announcement, not a peer-reviewed paper). Read on lilly.com
11. Eli Lilly and Company, press release, 23 July 2026 — topline results from the Phase 3 TRIUMPH-2 and TRIUMPH-3 trials, and the company’s plan to submit a Biologics License Application to the US FDA in the first quarter of 2027 (company announcement, not a peer-reviewed paper). Read on lilly.com

What a six-day half-life means for your record

A phase 1b pharmacokinetic study described a dose-proportional half-life of approximately 6 days, about 144 hours (Urva et al., Lancet 2022). A half-life is the time taken for half of what is present to clear, and at roughly six days the practical consequence is that weekly injections overlap heavily instead of clearing between them. Levels build across the early weeks rather than returning to zero, which is why trial designs settle on a weekly rhythm in the first place.

Two things follow for record-keeping. A missed week is a much larger gap than a missed day would be on a daily compound, so the log needs to make an absent week obvious at a glance rather than burying it. And because the curve is slow, effects and side effects observed in any given week are a product of several preceding weeks, not just the most recent injection — which makes the dated history far more informative than any single entry in it.

Why this page has no dosing section

Retatrutide is investigational. There is no approved label anywhere in the world, which means there is no authorised dosing, no approved titration path, and no clinician-facing guidance outside trial and expanded-access protocols. Any figure published as a “typical dose” for an unapproved compound is not drawn from an approved source, because no such source exists. It is drawn from forum consensus, from vendor copy, or from someone's reading of a trial protocol that was run under monitoring conditions that do not apply outside it.

Pepti is a record-keeping tool. It logs the figure you already have with the date, time, site and vial, and remembers where the last injection went. It does not supply the figure, and it will not, for this compound or any other. Pages that publish dose tables for investigational compounds are publishing folklore with the typography of evidence — the numbers look authoritative because they are set in a table, not because anything stands behind them. The figure belongs to you and whoever directs your use. The record is what we are for.

What a clean retatrutide record holds

Because the cadence is weekly, there are relatively few entries in a retatrutide log, which makes each one carry more weight. A record worth keeping holds the following.

The record-keeping method in full is set out in tracking a retatrutide schedule, and the free reconstitution calculator on this site (not the app) converts the figures you already have into a draw volume and a count of doses per vial. A peptide tracker app keeps your log, site sequence and vial records on one timeline, and the GLP-1 tracker covers what to log for a weekly injection.

Another compound in this reference series: cagrilintide.

Common questions

What is retatrutide?

Retatrutide is an investigational peptide that acts as a triple agonist at three receptors at once: GIP, GLP-1 and glucagon. The first two are shared with earlier incretin-class agents; the glucagon receptor is the addition that distinguishes it. It has been studied as a once-weekly subcutaneous injection in clinical trials.

Is retatrutide approved?

No. Retatrutide is not approved by any regulator, in any country, for any indication. The sponsor announced Phase 3 topline results from December 2025, peer-reviewed Phase 3 papers began to publish in 2026 (Bajaj et al., Lancet 2026; Jastreboff et al., NEJM 2026; Bellido et al., Lancet 2026), and the sponsor has said it plans to submit to the US FDA in the first quarter of 2027 (Eli Lilly, July 2026); a submission is not an approval. Further Phase 3 studies are listed as ongoing. Since June 2026 the sponsor has also listed a pre-approval, single-patient expanded-access programme on ClinicalTrials.gov (NCT07629401); expanded access is not an approval. Because it is unapproved there is no label, no authorised dosing, and no clinician-facing guidance for it outside trial and expanded-access protocols.

What is retatrutide's half-life?

Retatrutide's half-life is approximately 6 days (about 144 hours), per a phase 1b pharmacokinetic study (Urva et al., Lancet 2022). That is the reason a weekly cadence appears in trial designs: successive weekly injections overlap substantially rather than clearing between administrations.

How is retatrutide different from tirzepatide?

Tirzepatide is a dual agonist acting at GIP and GLP-1 receptors. Retatrutide adds a third target, the glucagon receptor. Trials report a mean body-weight reduction of 20.9 percent at 72 weeks for tirzepatide (Jastreboff et al., NEJM 2022) and 25.0 percent at 80 weeks for retatrutide in a Phase 3 obesity trial (Jastreboff et al., NEJM 2026), both in the highest-dose groups. These come from separate trials with different populations, durations and designs, so the figures are not a head-to-head comparison.

Does retatrutide need to be reconstituted?

It depends entirely on the form. Trial product is supplied as a solution, already in liquid form and requiring no mixing. Material circulating outside trials is commonly supplied as a lyophilized powder, which is inert until a diluent is added. These are two different physical products, and a record that does not say which one it describes is ambiguous later.

Does Pepti tell me what dose to take?

No. Pepti supplies no dose figures for retatrutide or for anything else. It records the figure you already have from whoever directs your use, with the date, time, injection site and vial, and keeps the 12-zone site sequence. The record is ours; the figure is not.

How long does retatrutide stay in your body?

The phase 1b study reported a half-life of approximately 6 days (Urva et al., Lancet 2022); there is no label, because the compound is investigational. Arithmetic on that figure: about half remains after 6 days, about 3 percent after five half-lives, roughly 30 days, and under 1 percent after seven. That is a population figure from a trial, not a prediction for any one person.

This page is a reference on published evidence and record-keeping. It does not recommend retatrutide or any other substance, and it provides no dose figure, no titration amount, and no schedule. Retatrutide is investigational and not approved for any use.

The Pepti peptide tracker for iPhone keeps the weekly log, the site sequence, the vial records and the weight trend in one place.

Not medical advice. Pepti is a record-keeping tool, not a medical device.

Pepti – Peptide Tracker · Compound index · Reviewed October 2026 · Editorial policy · About