Pinc PeptideThe girly peptide research blog

Retatrutide · Dose evidence · updated 8 October 2026

Retatrutide dosage: what studies actually used

The short answer

Retatrutide’s phase 3 trials started everyone at 2 mg once a week and raised the dose every 4 weeks to a target of 4, 9 or 12 mg once a week345. No dose is approved, because no regulator anywhere has approved retatrutide6. This page reports trial doses and is not dosing advice. Products sold online are another matter: only 1 of 18 samples tested in Australia in 2026 matched its label7.

Not dosing advice. This page reports doses that studies and approved labels used, with their sources. It does not recommend a dose, and we do not give mixing, injection or unit-conversion instructions. Gray-market vials often do not contain what their label says. How we report doses.

Every dose studied in people

StudyWhoPeopleDose and routeWhat happened
TRIUMPH-1 (Jastreboff 2026), randomized trial Adults with obesity, without diabetes 2,339 4, 9 or 12 mg once a week, after 4-week steps from 2 mg
Injection under the skin · 80 weeks		 Weight fell 17.6%, 23.7% and 25.0% on 4, 9 and 12 mg, versus 3.9% on placebo, counting people who stopped the drug; 4.1%, 6.9% and 11.3% stopped because of side effects, versus 4.9%13.
TRIUMPH-3 (Lilly press release 2026), randomized trial Adults with a BMI of 35 or more and established heart or blood-vessel disease 1,949 9 or 12 mg once a week, after 4-week steps from 2 mg
Injection under the skin · 80 weeks		 Weight fell 21.6% and 22.6%, versus 3.2% on placebo, in an analysis that assumes everyone stayed on treatment; 9.8% and 13.5% stopped because of side effects, versus 4.8%4.
TRIUMPH-2 (Bellido 2026), randomized trial Adults with obesity or overweight and type 2 diabetes 1,152 4, 9 or 12 mg once a week, after 4-week steps from 2 mg
Injection under the skin · 80 weeks		 Weight fell 11.9%, 16.8% and 18.8%, versus 5.1% on placebo, counting people who stopped the drug; 4%, 12% and 8% stopped because of side effects or death, versus 5%8.
TRANSCEND-T2D-1 (Bajaj 2026), randomized trial Adults with type 2 diabetes treated with diet and exercise alone 537 4, 9 or 12 mg once a week
Injection under the skin · 40 weeks		 Counting people who stopped the drug, HbA1c (a measure of average blood sugar) fell 1.69, 1.86 and 1.94 percentage points, versus 0.81 on placebo, and weight fell 11.5%, 13.9% and 15.3%, versus 2.6%9.
TRIUMPH-4 (Lilly press release 2025), randomized trial Adults with obesity or overweight and knee osteoarthritis, without diabetes 445 9 or 12 mg once a week, after 4-week steps from 2 mg
Injection under the skin · 68 weeks		 Weight fell 20.0% and 23.7%, versus 4.6% on placebo, counting people who stopped the drug, or 26.4% and 28.7%, versus 2.1%, in an analysis that assumes everyone stayed on treatment; 12.2% and 18.2% stopped because of side effects, versus 4.0%5.
Phase 2 obesity trial (Jastreboff 2023), randomized trial Adults with obesity, or overweight with a weight-related condition 338 1, 4, 8 or 12 mg once a week; 4 and 8 mg started at 2 or 4 mg, and 12 mg at 2 mg
Injection under the skin · 48 weeks		 Weight fell 8.7%, 17.1%, 22.8% and 24.2% on 1, 4, 8 and 12 mg at 48 weeks, versus 2.1% on placebo; digestive side effects rose with dose and were partly eased by starting at 2 mg rather than 4 mg10.
Phase 2 type 2 diabetes trial (Rosenstock 2023), randomized trial Adults with type 2 diabetes, in the USA 281 0.5, 4, 8 or 12 mg once a week, with different starting doses, versus dulaglutide 1.5 mg or placebo
Injection under the skin · 36 weeks		 On 12 mg, HbA1c fell 2.02 percentage points at 24 weeks, versus 0.01 on placebo and 1.41 on dulaglutide, and weight fell 16.94% at 36 weeks, versus 3.00% on placebo2.
Phase 1b trial (Urva 2022), randomized trial Adults with type 2 diabetes 72 0.5, 1.5 or 3 mg once a week, or 3 mg stepped up to 6 mg or to 12 mg
Injection under the skin · 12 weeks		 Blood sugar fell at the three highest doses, and weight fell by up to 8.96 kg more than on placebo on the schedule that reached 12 mg11.

Studies, animals and users: kept apart

Doses below are what studies used or what a label says. They are not advice, and gray-market products may not contain what their label says.

In human studies

No dose is approved. Phase 3 trials started everyone at 2 mg once weekly and raised the dose every 4 weeks (2, 4, 6, 9, then 12 mg) to a target of 4, 9 or 12 mg once weekly, injected under the skin; the 4 mg arm used a single step at 2 mg35. Phase 2 tested 1 to 12 mg weekly for 48 weeks; starting at 2 mg rather than 4 mg reduced stomach side effects10. The Phase 1b trial used 0.5 to 12 mg weekly for 12 weeks11.

In animal studies

Mice: 30 nmol/kg by subcutaneous injection every other day, in an obesity and cancer model12. Rats: single subcutaneous doses of 0.03, 0.1 and 0.3 mg/kg given 3 hours before alcohol, in a study of alcohol’s felt effects13. These are research doses in animals, not human doses.

What users report

No community dosing page was cited for this compound.

Half-life and how it is taken

Half-life
About 6 days11Phase 1b multiple-dose study in adults with type 2 diabetes (0.5 to 12 mg weekly for 12 weeks); supports once-weekly dosing
Routes
  • Subcutaneous injection once weekly (the only route in the human studies we found)
  • No human data found for any other route

Why the dose goes up slowly

Every phase 3 trial started at 2 mg once a week and moved up one step every 4 weeks, through 2, 4, 6 and 9 mg, until each person reached their assigned dose345. On that schedule the target doses began at set weeks3:

  • 4 mg from week 5, after 4 weeks on 2 mg3.
  • 9 mg from week 13, after 2, 4 and 6 mg3.
  • 12 mg from week 17, after 2, 4, 6 and 9 mg3.

In the phase 2 obesity trial, digestive side effects rose with dose and were partly eased by starting at 2 mg rather than 4 mg10. In the phase 2 type 2 diabetes trial, digestive side effects ranged from 13% on 0.5 mg to 50% on 8 mg started at 4 mg, and the authors say the results informed the choice of doses for phase 32.

What about a missed dose?

Retatrutide has no label, so there is no official rule for a missed dose6. In May 2026, Lilly said it was legally available only to people in its trials3; it now also offers single-patient early access, requested by a doctor, for some adults with severe obesity who cannot join a trial, a program it confirmed publicly on 3 August 20261415.

The labels of related approved drugs set different rules: Zepbound allows a missed dose within 4 days, while the Wegovy injection allows one only if the next dose is more than 2 days away1617. Neither label covers retatrutide1617.

What the higher doses add, and what they cost

In TRIUMPH-1, going from 4 mg to 12 mg added 7.4 percentage points of weight loss at 80 weeks (17.6% versus 25.0%, counting people who stopped the drug)1. Stopping because of side effects rose from 4.1% to 11.3%, and vomiting from 10.6% to 25.3%3.

In TRIUMPH-4, 18.2% of people on 12 mg stopped because of side effects, versus 4.0% on placebo; Lilly says these rates were closely linked to starting BMI (body mass index, weight relative to height) and included stops for perceived excessive weight loss5. Among people starting with a BMI of 35 or more, the rate on 12 mg was 12.1%, versus 4.8% on placebo5. Dysesthesia (tingling or other unusual skin sensations) affected 20.9% on 12 mg, versus 0.7% on placebo5.

Data beyond 80 weeks come from a Lilly press release3. A blinded 24-week extension of TRIUMPH-1, to 104 weeks in all, enrolled 532 people with a BMI of 35 or more who had finished the 80-week trial on their assigned dose3. Those first assigned to 12 mg had lost 29.9% of their weight on average by week 104, or 30.3% in an analysis that assumes everyone stayed on treatment3.

Why gray-market vials make doses unreliable

Every dose on this page was given in Lilly’s trials, with Lilly’s drug38. No medicine containing retatrutide is approved, and FDA says US pharmacies cannot compound it618. As of 30 September 2026, 63 of Finnrick’s latest 194 completed retatrutide tests failed, even though its pass mark allows the content to differ from the label by up to 35%1920.

Australian tests also found large dose errors7. Of 18 samples tested by Leeder Analytical in 2026, only 1 matched its label, about 30% were over strength, about 30% were under, and 1 contained no retatrutide7. In a published letter, Australian researchers reported three vials sold as retatrutide and labeled 10 mg that held 5.13 mg, 16.5 mg and 19.0 mg21. ABC News reported a safety advisory from Australia’s medicines regulator, the TGA: a person who used a product sold as retatrutide had vomiting so severe that it tore their esophagus, and TGA tests of the unmarked vial found no retatrutide but undeclared semaglutide2223.

Results outside trials look different too24. An analysis of 378 people using retatrutide from gray-market and other non-trial sources, not yet peer reviewed, reported 7.2% average weight loss at 12 months, versus 15.5% in trials at the same point24.

Questions people ask

How much retatrutide should I take?

No dose is approved, because retatrutide is not approved anywhere6. In phase 3 trials, everyone started at 2 mg once a week and stepped up every 4 weeks to a target of 4, 9 or 12 mg once a week34. Ask your prescriber about approved options.

What is the highest dose of retatrutide studied?

12 mg once a week, the top dose in the phase 2 and phase 3 trials310. The phase 1b trial also reached 12 mg, by stepping up from 3 mg within its 12 weeks11. The phase 3 program uses five doses: 2, 4, 6, 9 and 12 mg5.

How long does each retatrutide dose step last in trials?

Four weeks: in phase 3 trials, people took 2 mg for 4 weeks, then moved up one step every 4 weeks, through 4, 6 and 9 mg, until they reached their assigned dose345. On that schedule, 12 mg begins in week 173.

Does retatrutide work immediately?

Not all at once: in trials, weight loss built up over months10. In the phase 2 obesity trial, people on 12 mg had lost 17.5% of their weight at 24 weeks and 24.2% at 48 weeks10. In the 12-week phase 1b trial in type 2 diabetes, blood sugar had fallen by week 12 at the three highest doses11.

When will retatrutide be approved?

It is not approved anywhere yet6. Lilly plans to submit it for US approval in the first quarter of 2027, after completing the manufacturing data an application needs4. Lilly offers single-patient early access, requested by a doctor, to some adults with a BMI of 35 or more whose obesity has not responded to the highest available dose of a weight-management medicine, who have at least two serious complications and who cannot join a trial1415.

Go deeper

Sources

  1. 1Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity New England Journal of Medicine, 29 Sep 2026. pubmed.ncbi.nlm.nih.gov
  2. 2Retatrutide, 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 conducted in the USA The Lancet, 12 Aug 2023. pubmed.ncbi.nlm.nih.gov
  3. 3Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial Eli Lilly and Company (PR Newswire), 21 May 2026. prnewswire.com
  4. 4Lilly’s triple agonist, retatrutide, successful in two additional Phase 3 obesity trials, delivering significant improvements in weight and A1C Eli Lilly and Company (PR Newswire), 23 Jul 2026. prnewswire.com
  5. 5Lilly’s triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial Eli Lilly and Company (PR Newswire), 11 Dec 2025. prnewswire.com
  6. 6Lilly calls on online platforms, payment companies and regulators to shut down the illegal retatrutide black market Eli Lilly and Company (PR Newswire), 12 Aug 2026. prnewswire.com
  7. 7New testing of black market peptides reveals dangerous dosing levels ABC News (Australia), 28 Aug 2026. abc.net.au
  8. 8Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial The Lancet, 29 Sep 2026. pubmed.ncbi.nlm.nih.gov
  9. 9Efficacy 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, 13 Jun 2026. pubmed.ncbi.nlm.nih.gov
  10. 10Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial New England Journal of Medicine, 10 Aug 2023. pubmed.ncbi.nlm.nih.gov
  11. 11LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial The Lancet, 26 Nov 2022. pubmed.ncbi.nlm.nih.gov
  12. 12Incretin triple agonist retatrutide (LY3437943) alleviates obesity-associated cancer progression npj Metabolic Health and Disease, 2025. pubmed.ncbi.nlm.nih.gov
  13. 13Semaglutide, tirzepatide, and retatrutide attenuate the interoceptive effects of alcohol in male and female rats Psychopharmacology, May 2026. pubmed.ncbi.nlm.nih.gov
  14. 14Lilly Expands Retatrutide Access Amid Doctor Pushback AJMC (The American Journal of Managed Care), 5 Aug 2026. ajmc.com
  15. 15Pre-approval Expanded Access of Retatrutide (LY3437943), NCT07629401 ClinicalTrials.gov, 6 Aug 2026. clinicaltrials.gov
  16. 16ZEPBOUND (tirzepatide) injection, for subcutaneous use: prescribing information Eli Lilly and Company via DailyMed (U.S. National Library of Medicine), 28 Aug 2026. dailymed.nlm.nih.gov
  17. 17WEGOVY (semaglutide) injection and tablets: prescribing information (SPL version 19) Novo Nordisk via DailyMed (U.S. National Library of Medicine), 30 Jun 2026. dailymed.nlm.nih.gov
  18. 18FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss U.S. Food and Drug Administration, 1 Oct 2026. fda.gov
  19. 19Retatrutide: vendor test results Finnrick, 29 Sep 2026. finnrick.com
  20. 20Methodology Finnrick, accessed 30 Sep 2026. finnrick.com
  21. 21Composition and Labelling Accuracy of Products Sold as Retatrutide in Australia Drug and Alcohol Review, Sep 2026. pubmed.ncbi.nlm.nih.gov
  22. 22Patient suffers torn oesophagus after using unapproved peptide, prompting fresh warnings ABC News (Australia), 14 Sep 2026. abc.net.au
  23. 23TGA tests counterfeit retatrutide product following serious adverse event report Pharmacy Today, 15 Sep 2026. pharmacytoday.co.nz
  24. 24August 24, 2026: Study finds black market retatrutide is not as effective as the clinical trial versions Partnership for Safe Medicines, 24 Aug 2026. safemedicines.org

Not medical advice. Talk to a licensed clinician before using any drug. Report an error.