Retatrutide Dosage: What the Phase 2 and 3 Trials Used

What Retatrutide Is

Retatrutide, known in the research literature by its development code LY3437943, is a single peptide that acts on three receptors at once: the receptors for GIP, GLP-1, and glucagon.⁴ The trial papers describe it as a novel synthetic molecule and a triple hormone receptor agonist.⁷ In the lab it shows balanced activity at the glucagon and GLP-1 receptors and more activity at the GIP receptor.⁴ That triple action is why it is being studied for obesity and type 2 diabetes, and why the dose question is more interesting than it looks: the trials had to find a level that balanced effect against the side effects that come with hitting three pathways.

Two facts frame everything on this page. First, in every human study in this review the drug was given the same way, a subcutaneous injection, once weekly, which its reported half-life of about 6 days supports (phase 1b trial, PMID 36354040).¹³ Second, it is investigational. The FDA says retatrutide is not a component of any approved drug and has not been found safe and effective for any condition,¹² and the manufacturer itself calls it an investigational agent under clinical development.¹¹⁶

There is no approved label, so there is no approved dose. For when an approved version might actually arrive, see when will retatrutide be available. What exists is a set of trial arm assignments, and that is what follows. The retatrutide profile covers the molecule itself.

The Phase 2 Doses

The dose ladder started in a phase 1b study in people with type 2 diabetes. Over 12 weeks it ran once-weekly cohorts of 0.5 mg, 1.5 mg, and 3 mg, plus two escalation cohorts that stepped up to 6 mg and, in the top cohort, up to 12 mg (trial doses, not a recommendation, PMID 36354040).³ That study reported the roughly 6 day half-life behind weekly dosing and a placebo-adjusted weight reduction of up to 8.96 kg in the top escalation cohort (phase 1b trial, PMID 36354040). Those results set up the phase 2 programme.

Disclaimer: every dose in this table was assigned and monitored inside a clinical trial; none of it is a recommendation, a starting dose or a schedule to follow.

The phase 2 obesity trial is the one most people mean when they talk about retatrutide. It enrolled 338 adults with obesity and ran for 48 weeks, testing once-weekly maintenance doses of 1 mg, 4 mg, 8 mg, and 12 mg (trial doses, not a recommendation, PMID 37366315).¹ Several arms reached 4 mg and 8 mg from two different starting doses, a 2 mg start and a 4 mg start, which is why the published arm list looks more complicated than four numbers.

At 48 weeks the trial reported average weight reductions of about 8.7% at 1 mg, 17.1% at the combined 4 mg arms, 22.8% at the combined 8 mg arms, and 24.2% at 12 mg, against 2.1% on placebo (phase 2 trial, 48 weeks, PMID 37366315). The response climbed with the dose, which is exactly why the higher doses carried into phase 3.

The phase 2 type 2 diabetes trial ran in parallel. It randomised 281 adults across 42 US centres and tested once-weekly retatrutide at 0.5 mg, 4 mg, 8 mg, and 12 mg, alongside placebo and a dulaglutide comparator (trial doses, not a recommendation, PMID 37385280).² Its main measure was blood sugar: at 24 weeks HbA1c fell by up to 2.02% at 12 mg versus almost no change on placebo, and body weight fell by up to about 16.9% at 12 mg by 36 weeks (phase 2 trial, PMID 37385280). The authors say plainly that this trial informed the dose selection for the phase 3 programme, which is the thread that leads to the 4, 9, and 12 mg you see later.

A substudy of the obesity trial looked at liver fat at the same 1, 4, 8, and 12 mg doses, and the dose-response was steep: relative liver fat reductions of about 42.9% at 1 mg rising to 82.4% at 12 mg by 24 weeks (phase 2a substudy, PMID 38858523).⁵ Across all of these arms, the two different starting doses were not a menu, they were a measurement. The trial found that the lower 2 mg start partially reduced the gastrointestinal side effects, which is a finding about tolerability, not a protocol.¹

Sources: TRIUMPH-2, The Lancet, 29 September 2026; TRIUMPH-1, New England Journal of Medicine, 29 September 2026; Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026

The Phase 3 Doses

The flagship obesity trial, TRIUMPH-1, published its doses in the New England Journal of Medicine on 29 September 2026: 2,339 adults with obesity, or overweight plus a weight-related condition, and no diabetes were randomised to once-weekly retatrutide at 4 mg, 9 mg, or 12 mg, or placebo, for 80 weeks (trial doses, not a recommendation). In TRIUMPH-1, Lilly reported that every retatrutide arm started at 2 mg and stepped up every four weeks: 4 mg after one step at 2 mg, 9 mg through 2, 4, and 6 mg, and 12 mg through 2, 4, 6, and 9 mg (trial schedule, not a recommendation). For the TRIUMPH-1 treatment-regimen estimand, which counts everyone randomised, mean body weight changed by -17.6% at 4 mg, -23.7% at 9 mg, and -25.0% at 12 mg, against -3.9% on placebo at 80 weeks.

TRIUMPH-2 used the same three trial arms in 1,152 adults with obesity or overweight and type 2 diabetes, and was published in The Lancet the same day. For the TRIUMPH-2 treatment-regimen estimand, mean body weight changed by -11.9% at 4 mg, -16.8% at 9 mg, and -18.8% at 12 mg, against -5.1% on placebo, at week 80. In TRIUMPH-3, Lilly reported 9 mg and 12 mg trial targets reached by the same four-week steps from 2 mg in 1,949 adults with a BMI of 35 or higher and established cardiovascular disease (trial doses, not a recommendation). Lilly reported TRIUMPH-3 efficacy-estimand weight changes of -21.6% at 9 mg and -22.6% at 12 mg against -3.2% on placebo at 80 weeks; these company results have not been peer reviewed.

The diabetes programme published first. TRANSCEND-T2D-1, a 40-week type 2 diabetes trial run across 48 sites in the USA, Mexico, and India, randomised 537 adults to once-weekly retatrutide at 4 mg, 9 mg, or 12 mg, or placebo (trial doses, not a recommendation, PMID 42250575).⁶ At 40 weeks it reported HbA1c falling further at higher doses and average weight reductions of about 11.5% at 4 mg, 13.9% at 9 mg, and 15.3% at 12 mg, against 2.6% on placebo (phase 3 trial, 40 weeks, PMID 42250575).

TRIUMPH-4 is a phase 3, 68-week stand-alone trial in adults who have obesity or overweight and osteoarthritis of the knee. Its doses are not in a journal paper but in preliminary results the manufacturer posted to its medical information site: its 445 participants were randomised 1:1:1 to retatrutide escalated to a 9 mg or 12 mg maximum, or placebo, each started at 2 mg and titrated at 4-week intervals (trial doses, not a recommendation, Lilly Medical Information).¹⁵¹⁰ Those preliminary results reported average weight reductions of about 26.4% at 9 mg and 28.7% at 12 mg, against 2.1% on placebo (phase 3 trial, 68 weeks, Lilly Medical Information). Lilly announced those results on 11 December 2025 and said detailed results would follow at a medical meeting and in a journal; no TRIUMPH-4 results paper was found in PubMed or Europe PMC as of 6 October 2026.

The 9 mg dose is worth pausing on, because it is new: it does not appear as a maintenance dose in any phase 2 retatrutide arm. The only earlier place a 9 is visible at all is as a transit step inside the phase 1b escalation ladder that stepped up to 12 mg.³ So 9 mg is a phase 3 dose level, chosen for these trials, not something carried over from the phase 2 work. That is a small detail with a large lesson: the doses that reach late-stage trials are engineered choices, not round numbers a reader can back into.

Disclaimer: every dose in this section was assigned and monitored inside a clinical trial; none of it is a recommendation, a starting dose or a schedule to follow.

Disclosure: Some links on this page are referral links. Peptides Vietnam may earn a fee at no cost to you. Editorial content is never sold.

Our supply partner lists retatrutide as a research compound on Peptara's retatrutide page. A research listing is not an approved medicine, and nothing on it turns the trial doses above into a dose to take.

Sources: ClinicalTrials.gov, TRIUMPH-4, NCT05931367; TRIUMPH-2, The Lancet, 29 September 2026; TRIUMPH-1, New England Journal of Medicine, 29 September 2026; Eli Lilly, TRIUMPH-1 results and trial design, 21 May 2026; Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026; Eli Lilly, TRIUMPH-4 topline results, 11 December 2025

The Phase 3 Obesity Doses

The obesity side of phase 3 is where the honest answer gets uncomfortable. The registrational obesity programme, called TRIUMPH, is four phase 3 trials in over 5,800 participants, all using weekly subcutaneous retatrutide against placebo.⁷ The design paper states the route and the schedule and no milligram figure for any arm. The ClinicalTrials.gov records do the same: the arms are labelled only Retatrutide Dose 1, Dose 2, and Dose 3, and the intervention is described only as administered subcutaneously.¹⁰

That registry masking is consistent across the whole registered phase 3 programme, TRIUMPH-4 included. What is public did not come from the registry. The milligram doses reached the public record through the journals and the company: TRIUMPH-1 in the New England Journal of Medicine and TRIUMPH-2 in The Lancet, both published online on 29 September 2026, TRIUMPH-3 in a July 2026 company release, TRIUMPH-4 on the manufacturer's medical information site, and the diabetes doses in the TRANSCEND-T2D-1 paper. Some phase 3 trials go further and use no fixed dose at all: the 10,000 participant cardiovascular and kidney outcomes trial escalates each participant to a maximum tolerated dose,¹⁰ and the phase 2b kidney study did the same, up to 12 mg.⁸

This is the part a dosage page has to be straight about. The phase 3 obesity doses are public now: in TRIUMPH-1, the New England Journal of Medicine paper reports trial arms of 4, 9 and 12 mg once weekly, and Lilly describes four-week steps from 2 mg under investigator monitoring (trial doses, not a recommendation). They are not an approved dose, because none exists, and this page will not turn a trial arm into a schedule for anyone to follow. For how the phase 2 results line up against an approved drug, see retatrutide vs tirzepatide.

Sources: TRIUMPH-2, The Lancet, 29 September 2026; TRIUMPH-1, New England Journal of Medicine, 29 September 2026; Eli Lilly, TRIUMPH-1 results and trial design, 21 May 2026; Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026; Eli Lilly, TRIUMPH-4 topline results, 11 December 2025

Disclaimer: this is general education, not medical advice and not a dosing recommendation.

What the Trials Reported

Dose and side effects are linked here, which is the whole reason the trials escalated so carefully. Across the studies the most common adverse events were gastrointestinal, mostly mild to moderate, and they tracked with the dose.¹ In the phase 2 type 2 diabetes trial, gastrointestinal events ranged from about 13% of participants in the lowest 0.5 mg group to about 50% in one of the fast-escalation 8 mg groups, with no severe hypoglycaemia and no deaths reported (phase 2 trial, PMID 37385280).² The obesity trial also reported dose-dependent increases in heart rate that peaked at 24 weeks and then declined (phase 2 trial, PMID 37366315).

The phase 3 type 2 diabetes trial reported the same general pattern: mostly mild to moderate gastrointestinal events that subsided over time, discontinuations for adverse events of roughly 2 to 5% on retatrutide versus none on placebo, no severe hypoglycaemia, and two deaths, both in the 4 mg group and both judged unrelated to the study drug (phase 3 trial, PMID 42250575).⁶ None of this is a safety verdict for use outside a trial. It is what investigators observed under monitoring at fixed, assigned doses.

Disclaimer: this is general education, not medical advice and not a dosing recommendation.

Why This Is Not a Dose to Copy

Everything above is a trial arm, and a trial arm is not a prescription. Retatrutide has no approved label anywhere in this review, so there is no sanctioned dose, no titration schedule, and no approved indication to frame one.¹² The FDA has been explicit: retatrutide cannot be used in compounding under federal law, and it has warned companies selling it under research use only or not for human consumption labelling, and telehealth companies marketing it directly to consumers.¹² There is a named, dated enforcement record to match, a March 2026 FDA warning letter to a peptide seller offering retatrutide as an unapproved new drug.¹³

One product record can look like an exception to that, and it is worth naming so it is not mistaken for one. DailyMed, the drug label repository run by the US National Library of Medicine, carries a set of Structured Product Labeling records for a retatrutide product branded SALKALLI, with pen strengths listed as high as 40 mg and a titration of 2.5 mg, 5 mg, 7.5 mg, then 10 mg once weekly (export filing figures, not a trial dose and not a recommendation).¹⁶ That is not an FDA approval. Every one of those records was filed by a single labeler, Guangzhou Yixin Cross-border E-commerce Co., Ltd., and every one is marked as export only, which is a filing the registrant itself submits, not a review or an authorisation by the FDA.¹⁶

The tell is in the numbers: that 2.5, 5, 7.5 and 10 mg ladder, and the pen strengths up to 40 mg, match no retatrutide trial fetched for this page, whose arms ran from 0.5 mg to 12 mg with a 2 mg or 4 mg start. A schedule that turns up on the export filing of a cross-border seller and in none of the trials is not a schedule to copy.

Why does the exact number matter so much? Because with this class of drug, dosing errors have already put people in hospital. The FDA has reported adverse events, some requiring hospitalisation, from dosing errors with compounded semaglutide, a different GLP-1 drug, where patients or clinicians measured and injected the wrong amount.¹² That is a semaglutide finding, not a retatrutide one, but it is the clearest illustration of why a milligram figure lifted from a trial is not something to reverse-engineer at home.

There is exactly one supervised route to retatrutide outside a clinical trial, and it is narrow: the manufacturer runs a pre-approval expanded access programme for adults with severe obesity, a body mass index of 35 or higher, and at least two serious obesity-related complications, who are refractory to approved therapy and cannot join a trial.¹¹ It is not a shortcut to a dose. And where people reach for animal data to justify a number, the animal record does not supply one either: the discovery paper reports that retatrutide reduced body weight in obese mice but states no dose (mouse study, PMID 35985340),⁴ and the one isolated-tissue study used a fixed concentration of 100 nM in a mouse atrial preparation, not an injected dose in a living animal (animal study, isolated mouse atria, not an in vivo route, PMID 40464942).⁹

On availability closer to home, this review could not confirm a Vietnamese pharmacy listing, a price, or a registration number with the Drug Administration of Vietnam, but most of those checks were blocked or inconclusive rather than clean negatives, so nothing here should be read as saying retatrutide is unavailable or unregistered in Vietnam.¹⁴ The right move is to confirm the current status directly with the Drug Administration of Vietnam. For the neighbouring GLP-1 drug that is further along the approval path, the semaglutide in Vietnam guide covers the same regulatory ground in more depth. Local access and legality are covered in the retatrutide in Vietnam guide.

Disclaimer: this is general education, not medical advice and not a dosing recommendation.

The Short Version

For our supply partner Peptara Labs's own write-up on the same question, see Peptara's retatrutide dosage page, and read it next to the trial record above rather than instead of it.

Sources: TRIUMPH-2, The Lancet, 29 September 2026; TRIUMPH-1, New England Journal of Medicine, 29 September 2026; Eli Lilly, TRIUMPH-1 results and trial design, 21 May 2026; Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026; Eli Lilly, TRIUMPH-4 topline results, 11 December 2025; ClinicalTrials.gov, retatrutide trial records

Sources and references

1. 1.Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine, 2023. ClinicalTrials.gov NCT04881760. PMID 37366315. PubMed PMID 37366315
2. 2.Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial. The Lancet, 2023. NCT04867785. PMID 37385280. PubMed PMID 37385280
3. 3.LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b multiple-ascending dose trial. The Lancet, 2022. NCT04143802. PMID 36354040. PubMed PMID 36354040
4. 4.LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metabolism, 2022. PMID 35985340. PubMed PMID 35985340
5. 5.Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine, 2024. NCT04881760. PMID 38858523. PubMed PMID 38858523
6. 6.Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. The Lancet, 2026. NCT06354660. PMID 42250575. PubMed PMID 42250575
7. 7.Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism, 2026. PMID 41090431. PubMed PMID 41090431
8. 8.Rationale, design and baseline characteristics of the TRANSCEND-CKD trial of retatrutide in patients with chronic kidney disease. Nephrology Dialysis Transplantation, 2026. NCT05936151. PMID 41160422. PubMed PMID 41160422
9. 9.Contractile effects of retatrutide in isolated mouse atrial preparations. Naunyn Schmiedebergs Archives of Pharmacology, 2025. PMID 40464942. PubMed PMID 40464942
10. 10.ClinicalTrials.gov, retatrutide trial registry. Phase 2 and phase 3 records, arm labels and enrolments, fetched via the public API v2, 2026. clinicaltrials.gov / retatrutide
11. 11.Pre-approval Expanded Access of Retatrutide (LY3437943). ClinicalTrials.gov NCT07629401. Sponsor Eli Lilly and Company, status Available. clinicaltrials.gov / NCT07629401
12. 12.US Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. Content current as of 09/01/2026. fda.gov / unapproved GLP-1 drugs
13. 13.US Food and Drug Administration. Warning Letter to Gram Peptides, reference 721806, March 31, 2026. fda.gov / warning letter 721806
14. 14.Drug Administration of Vietnam, Ministry of Health. Public service portal for drug registration and price management. dichvucong.dav.gov.vn
15. 15.Eli Lilly. What are the preliminary results with retatrutide from TRIUMPH-4 in participants with obesity or overweight and osteoarthritis? Lilly Medical Information (US). ClinicalTrials.gov NCT05931367. Fetched 2026-09-06. medical.lilly.com / TRIUMPH-4 preliminary results
16. 16.DailyMed, US National Library of Medicine. Structured Product Labeling records for retatrutide (brand SALKALLI), labeler Guangzhou Yixin Cross-border E-commerce Co., Ltd., marketing category Export only, published Nov 17, 2025. Fetched 2026-09-06. dailymed.nlm.nih.gov / retatrutide SPL
17. 17.ClinicalTrials.gov, TRIUMPH-4, NCT05931367 ClinicalTrials.gov, TRIUMPH-4, NCT05931367
18. 18.TRIUMPH-2, The Lancet, 29 September 2026 TRIUMPH-2, The Lancet, 29 September 2026
19. 19.TRIUMPH-1, New England Journal of Medicine, 29 September 2026 TRIUMPH-1, New England Journal of Medicine, 29 September 2026
20. 20.Eli Lilly, TRIUMPH-1 results and trial design, 21 May 2026 Eli Lilly, TRIUMPH-1 results and trial design, 21 May 2026
21. 21.Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026 Eli Lilly, TRIUMPH-2 and TRIUMPH-3 results, 23 July 2026
22. 22.Eli Lilly, TRIUMPH-4 topline results, 11 December 2025 Eli Lilly, TRIUMPH-4 topline results, 11 December 2025