Pinc PeptideThe girly peptide research blog

Compare · updated 8 October 2026

Retatrutide vs tirzepatide

The short answer

In separate trials, retatrutide caused more weight loss than tirzepatide: 25.0% of body weight after 80 weeks on 12 mg, versus 20.9% after 72 weeks on tirzepatide 15 mg14. There is no head-to-head result yet: the trial that compares them directly, TRIUMPH-5, has an estimated primary completion date of November 20265. Tirzepatide is an FDA-approved medicine (Zepbound and Mounjaro), while retatrutide is not approved anywhere in the world67. Vials sold online as retatrutide often fail tests: as of 30 September 2026, 63 of Finnrick’s latest 194 completed tests failed8.

At a glance

ComparedRetatrutideTirzepatide
Evidence tierA Two or more large human trialsA Two or more large human trials
Does it work?For weight loss in obesity or overweight: Benefit shownIn a large trial, people without diabetes lost 25% of their weight on average over 80 weeks on the top dose, versus 3.9% on placebo9. It is not approved anywhere7.For weight loss and weight maintenance: Benefit shownIn a large trial, people lost 20.9% of their weight on average over 72 weeks on the top dose, versus 3.1% on placebo4. Weight tends to return after stopping10.
FDANot approved for any use7Approved (Zepbound, Mounjaro)6
US pharmaciesPharmacies may not make it11Copies limited since the shortage ended12
SportNot named; likely caught by the catch-all ban13Not banned, but monitored1314
AustraliaNot named in the Poisons Standard15Prescription only15
Half-lifeAbout 6 days16About 5 to 6 days17
Taken asSubcutaneous injection once weekly (the only route in the human studies we found)
No human data found for any other route		Subcutaneous injection, once weekly (the only approved route and the route used in all trials cited here)
Receptors it switches onThree: the receptors for the gut hormones GIP and GLP-1, which tirzepatide also targets, plus the glucagon receptor18.Two: the receptors for the gut hormones GIP and GLP-117.
Approved products and usesNone: on 12 August 2026, Lilly said no regulator anywhere had approved a medicine containing retatrutide7. Lilly plans to apply for US approval in the first quarter of 202719.Zepbound: weight reduction and long-term maintenance in adults, and moderate to severe obstructive sleep apnea in adults with obesity17. Mounjaro: type 2 diabetes, and heart risk reduction in adults with type 2 diabetes at high risk20.
Main phase 3 weight-loss trial (no diabetes)TRIUMPH-1, 2,339 adults, 80 weeks: weight fell 17.6%, 23.7% and 25.0% on 4, 9 and 12 mg a week, versus 3.9% on placebo1.SURMOUNT-1, 2,539 adults, 72 weeks: weight fell 15.0%, 19.5% and 20.9% on 5, 10 and 15 mg a week, versus 3.1% on placebo4.
Weight loss with type 2 diabetesTRIUMPH-2, 1,152 adults, 80 weeks: weight fell 11.9%, 16.8% and 18.8% on 4, 9 and 12 mg, versus 5.1% on placebo21.SURMOUNT-2, 938 adults, 72 weeks: weight fell 12.8% and 14.7% on 10 and 15 mg, versus 3.2% on placebo2.
Common side effects at the top doseTRIUMPH-1, 12 mg: nausea 42.4%, diarrhea 32.0%, constipation 26.1% and vomiting 25.3%, versus 14.8%, 13.5%, 10.9% and 4.8% on placebo9.Zepbound label, 15 mg: nausea 28%, diarrhea 23%, constipation 11% and vomiting 13%, versus 8%, 8%, 5% and 2% on placebo17.
Dysesthesia (unusual skin sensations)5.1% to 12.5% on 4 to 12 mg versus 0.9% on placebo in TRIUMPH-1, and 20.9% on 12 mg in TRIUMPH-4922.0.2% to 0.4% on 5 to 15 mg versus 0.1% on placebo in the Zepbound weight-loss trials17.
Stopped because of side effectsTRIUMPH-1: 4.1%, 6.9% and 11.3% on 4, 9 and 12 mg, versus 4.9% on placebo9.SURMOUNT-1: 4.3%, 7.1% and 6.2% on 5, 10 and 15 mg, versus 2.6% on placebo4.
Heart-outcome dataTRIUMPH-3, 1,949 adults with severe obesity and established heart or blood-vessel disease: heart events were rarer than expected in both groups, and the result was inconclusive (hazard ratio 0.82, 95% confidence interval 0.55 to 1.22, for a five-part measure of heart events and death)19.SURPASS-CVOT, 13,299 adults with type 2 diabetes and heart disease, followed for a median of about 4 years: as good as dulaglutide, an older GLP-1 drug, at preventing heart attack, stroke or cardiovascular death, but not shown to be better2324.
Gray-market vials63 of Finnrick’s latest 194 completed tests failed (32.5%) as of 30 September 20268. In Australia, only 1 of 18 samples tested in 2026 matched its label25.59 of Finnrick’s latest 196 completed tests failed (30.1%) as of 30 September 202626. Two counterfeit tirzepatide pens detained in Ireland contained insulin27.

How they work differently

Tirzepatide switches on the receptors for two gut hormones: GLP-1, which helps regulate appetite and calorie intake, and GIP, which lab and animal studies suggest adds to that effect17. Retatrutide switches on the same two plus a third, the receptor for glucagon18. In obese mice, the GIP and GLP-1 activity cut calorie intake, and the glucagon activity added weight loss by raising the energy the body burns18.

How much weight do people lose on each?

The head-to-head trial, TRIUMPH-5, had not finished at its last registry update, so today’s numbers come from separate trials5. TRIUMPH-1 ran for 80 weeks and SURMOUNT-1 for 72 weeks, and both enrolled adults with obesity, or overweight with a weight-related condition, who did not have diabetes49. TRIUMPH-1 participants also started heavier on average: 112.7 kg with a BMI of 40.0, against 104.8 kg and 38.0 in SURMOUNT-149. Because of these differences, the gap between 25.0% and 20.9% is not a like-for-like comparison14.

Both of those figures use the treatment-regimen estimand, which counts everyone who was randomized, including people who stopped the drug14. Lilly’s headline figure for retatrutide, 28.3% on 12 mg, uses the efficacy estimand instead, which estimates the result had everyone stayed on treatment9.

Retatrutide’s phase 2 trial pointed the same way: in 338 adults with obesity, 12 mg cut weight by 24.2% at 48 weeks, versus 2.1% on placebo28. The head-to-head trial, TRIUMPH-5, plans to enroll about 800 adults with obesity, randomly assigned to retatrutide or tirzepatide, and measures weight change at 80 weeks5. Outside trials, an analysis of 378 people using retatrutide from gray-market and other non-trial sources, not yet peer reviewed, reported average weight loss of 7.2% at 12 months, versus 15.5% in trials at the same point29.

Which causes more side effects?

TRIUMPH-5 had not reported results at its last registry update, so side-effect rates also come from separate trials5. The Zepbound label warns that side-effect rates from one drug’s trials cannot be directly compared with rates from another drug’s trials17. With that caveat, nausea was reported by 42.4% on retatrutide 12 mg in TRIUMPH-1 and by 28% on Zepbound 15 mg in its label trials917.

Dysesthesia, meaning unusual skin sensations such as tingling or pain, stands out on retatrutide: up to 12.5% in TRIUMPH-1 and 20.9% on 12 mg in TRIUMPH-4, against 0.4% or less on Zepbound91722. Lilly said most cases were mild to moderate and most resolved during treatment9.

Stopping because of side effects rose with the retatrutide dose, to 11.3% on 12 mg in TRIUMPH-1 and 18.2% on 12 mg in TRIUMPH-4, where Lilly said the stops included some for perceived excessive weight loss922. In retatrutide’s phase 2 trial, heart rate also rose with dose, peaking at 24 weeks28.

Why gray-market retatrutide is a different risk

Because no medicine containing retatrutide is approved, Lilly says none can be sold to consumers, and FDA says retatrutide cannot be used in compounding under federal law711. Tirzepatide, by contrast, is sold as an approved medicine6.

Tests of retatrutide sold outside trials show wide swings: in Australia, only 1 of 18 samples matched its label, and a vial labeled 10 mg held 19 mg2530. Victoria’s health department linked six cases of acute liver injury to products labeled retatrutide, possibly from a contaminant, and a seventh case followed3132.

Demand is high: retatrutide made up 34.6% of the test requests Finnrick received from May 2025 to May 202633. FDA warning letters of 24 August 2026 quoted product names such as “GLP-3 RT (Retatrutide) Research Peptide” and cited sellers’ blog-style “tirzepatide vs retatrutide” comparisons as evidence that their products were meant for people343536.

Questions people ask

Is retatrutide the same as tirzepatide?

No: they are different molecules, both made by Eli Lilly9. Tirzepatide switches on two hormone receptors, GIP and GLP-1, and is approved as Zepbound and Mounjaro; retatrutide adds a third, the glucagon receptor, and is not approved anywhere671718.

Is retatrutide the same as Ozempic?

No. Ozempic is semaglutide, a modified form of the gut hormone GLP-1 that switches on the GLP-1 receptor, and it is FDA-approved3738. Retatrutide switches on the GIP and glucagon receptors as well, and it is not approved anywhere718.

What is more powerful than tirzepatide?

In separate trials, retatrutide caused more weight loss: 25.0% at 80 weeks on 12 mg, versus 20.9% at 72 weeks on tirzepatide 15 mg14. The trial comparing them directly, TRIUMPH-5, has an estimated primary completion date of November 2026, and retatrutide is not approved anywhere57. Against semaglutide, the head-to-head SURMOUNT-5 trial found tirzepatide caused more weight loss39.

Can I go from tirzepatide to retatrutide?

No label gives directions for this, because retatrutide is not approved anywhere7. The head-to-head TRIUMPH-5 trial excluded people who had taken weight-loss drugs in the 90 days before screening, so it does not study a switch5. The Zepbound label advises against combining tirzepatide with any GLP-1 receptor agonist, and retatrutide acts on that receptor too1718.

Does retatrutide burn fat or muscle?

It reduces both, according to a phase 2 body-scan substudy in people with type 2 diabetes: fat mass fell by up to 26.1% at 36 weeks, versus 4.5% on placebo3. The authors wrote that the share of weight lost as lean mass, which includes muscle, was similar to other obesity treatments; 103 of the 189 people in the substudy finished treatment with both scans3. For tirzepatide, the Zepbound label says weight loss involves more fat loss than lean loss17.

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. 2Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial The Lancet, 19 Aug 2023. pubmed.ncbi.nlm.nih.gov
  3. 3Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial The Lancet Diabetes & Endocrinology, Aug 2025. pubmed.ncbi.nlm.nih.gov
  4. 4Tirzepatide Once Weekly for the Treatment of Obesity New England Journal of Medicine, 21 Jul 2022. pubmed.ncbi.nlm.nih.gov
  5. 5A Study of Retatrutide (LY3437943) Compared to Tirzepatide (LY3298176) in Adults Who Have Obesity (TRIUMPH-5), NCT06662383 ClinicalTrials.gov, 20 Jul 2026. clinicaltrials.gov
  6. 6Drugs@FDA via openFDA: approval history for NDA 215866 (Mounjaro) and NDA 217806 (Zepbound) U.S. Food and Drug Administration (openFDA), accessed 1 Oct 2026. api.fda.gov · data query
  7. 7Lilly 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
  8. 8Retatrutide: vendor test results Finnrick, 29 Sep 2026. finnrick.com
  9. 9Lilly’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
  10. 10Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial JAMA, 2 Jan 2024. pubmed.ncbi.nlm.nih.gov
  11. 11FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss U.S. Food and Drug Administration, 1 Oct 2026. fda.gov
  12. 12FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize U.S. Food and Drug Administration, 1 Apr 2026. fda.gov
  13. 13World Anti-Doping Code International Standard: Prohibited List 2026 World Anti-Doping Agency, 24 Sep 2025. wada-ama.org
  14. 14The 2026 Monitoring Program World Anti-Doping Agency, Sep 2025. wada-ama.org
  15. 15Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327) Federal Register of Legislation, Australian Government, 28 Sep 2026. legislation.gov.au
  16. 16LY3437943, 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
  17. 17ZEPBOUND (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
  18. 18LY3437943, 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, 6 Sep 2022. pubmed.ncbi.nlm.nih.gov
  19. 19Lilly’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
  20. 20MOUNJARO (tirzepatide) injection, for subcutaneous use: prescribing information Eli Lilly and Company via DailyMed (U.S. National Library of Medicine), 27 Aug 2026. dailymed.nlm.nih.gov
  21. 21Retatrutide 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
  22. 22Lilly’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
  23. 23Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes New England Journal of Medicine, 18 Dec 2025. pubmed.ncbi.nlm.nih.gov
  24. 24FDA approves Lilly’s Mounjaro (tirzepatide) to reduce cardiovascular risk in adults with type 2 diabetes Eli Lilly and Company (PR Newswire), 28 Aug 2026. prnewswire.com
  25. 25New testing of black market peptides reveals dangerous dosing levels ABC News (Australia), 28 Aug 2026. abc.net.au
  26. 26Tirzepatide: vendor test results Finnrick, 29 Sep 2026. finnrick.com
  27. 27HPRA health warning after detention of counterfeit tirzepatide pens containing insulin Health Products Regulatory Authority (Ireland), 10 Oct 2025. hpra.ie
  28. 28Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial New England Journal of Medicine, 10 Aug 2023. pubmed.ncbi.nlm.nih.gov
  29. 29August 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
  30. 30Vial of unapproved peptide retatrutide had double the strength indicated on label ABC News (Australia), 27 Jun 2026. abc.net.au
  31. 31Toxicity linked to unapproved peptide product labelled Retatrutide Department of Health, Victoria, 19 Jun 2026. health.vic.gov.au
  32. 32Doctors fear possible contaminated counterfeit peptide batch after seventh case of acute liver damage ABC News (Australia), 24 Aug 2026. abc.net.au
  33. 33We’d Rather Buy the Future Than Wait For It Finnrick, 10 Jun 2026. finnrick.com
  34. 34Warning letter to NuScience Peptides LLC (MARCS-CMS 733652) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  35. 35Warning letter to Peptide Partners LLC (MARCS-CMS 735063) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  36. 36Warning letter to Royal Peptides LLC (MARCS-CMS 734884) U.S. Food and Drug Administration, 24 Aug 2026. fda.gov
  37. 37Drugs@FDA: applications containing semaglutide (NDA 209637, 213051, 213182, 215256, 218316; ANDA 220314) U.S. Food and Drug Administration (openFDA), 29 Sep 2026. api.fda.gov · data query
  38. 38WEGOVY (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
  39. 39Tirzepatide as Compared with Semaglutide for the Treatment of Obesity New England Journal of Medicine, 3 Jul 2025. pubmed.ncbi.nlm.nih.gov

Not medical advice. Neither compound is recommended here. How we grade evidence · Report an error.