Retatrutide vs Tirzepatide: How the Trial Results Compare in 2026
Retatrutide vs tirzepatide: how the experimental triple agonist compares with Zepbound and Mounjaro in the TRIUMPH and SURMOUNT trials, weight loss on matched terms, stopping rates, side effects, and when it could be available.
Tirzepatide (sold as Zepbound and Mounjaro) is an FDA-approved dual GIP and GLP-1 receptor agonist. Retatrutide is an investigational triple agonist that also targets the glucagon receptor. In separate phase 3 trials, retatrutide's top dose produced more weight loss: 28.3% at 80 weeks vs 22.5% at 72 weeks on the same estimand [1][9]. No head-to-head result has been reported yet, and retatrutide cannot be legally sold [2].
As of September 30, 2026, this comparison includes the TRIUMPH-2 results presented at EASD. Safety details are in our page on retatrutide side effects.
In this guide you will learn:
- How the two mechanisms differ
- How phase 3 weight loss compares on matched terms
- What the head-to-head trial will answer
- How side effects and heart data compare
- Where retatrutide stands with the FDA
This page gives no retatrutide doses, switching advice, or sources.
Table of Contents
- Retatrutide vs Tirzepatide at a Glance
- How Retatrutide and Tirzepatide Work: Triple vs Dual Agonist
- Weight Loss: TRIUMPH-1 vs SURMOUNT-1
- Retatrutide vs Tirzepatide in Type 2 Diabetes: TRIUMPH-2 and SURMOUNT-2
- TRIUMPH-5: The Head-to-Head Trial
- Stopping Rates and Side Effects in TRIUMPH-1 vs SURMOUNT-1
- Evidence Beyond Weight Loss
- Muscle, Protein, and Eating Well on Tirzepatide Now
- Semaglutide, Tirzepatide, and Retatrutide Compared
- When Could Retatrutide Be Available? Filing Plan and Expanded Access
- Which Is Right for You Now?
- Frequently Asked Questions
- Key Takeaways
Retatrutide vs Tirzepatide at a Glance
Retatrutide vs tirzepatide comes down to one extra target and one big status gap. Tirzepatide acts on two receptors and has FDA approval; retatrutide acts on three and is still in trials [2][12].
| Feature | Retatrutide | Tirzepatide |
|---|---|---|
| Receptors | GIP, GLP-1, and glucagon | GIP and GLP-1 |
| FDA status | Investigational, not approved | Approved: Mounjaro (May 2022), Zepbound (November 2023) |
| Brand names | None | Zepbound, Mounjaro |
| How it is given | Once-weekly injection in trials | Once-weekly injection |
| Main obesity trial | TRIUMPH-1: 2,339 adults, 80 weeks | SURMOUNT-1: 2,539 adults, 72 weeks |
| Top-dose weight loss, efficacy estimand | 28.3% | 22.5% |
| Top-dose weight loss, treatment-regimen estimand | 25.0% | 20.9% |
| Stopped for side effects, top dose vs placebo | 11.3% vs 4.9% | 6.2% vs 2.6% |
| Heart outcomes data | TRIUMPH-3 inconclusive; outcomes trial primary completion estimated 2029 | Mounjaro approved to lower major cardiovascular event risk in type 2 diabetes |
| Who can get it now | Trial participants or physician-requested expanded access | People with a prescription for an approved use |
Sources: Lilly releases, SURMOUNT-1, Zepbound and Mounjaro labels, ClinicalTrials.gov [1][2][4][8][9][12][14][18][19].
Our Zepbound vs Mounjaro comparison explains the two tirzepatide brands.
How Retatrutide and Tirzepatide Work: Triple vs Dual Agonist
Retatrutide and tirzepatide both activate GIP and GLP-1 receptors, and retatrutide also activates the glucagon receptor. Lilly describes retatrutide as "a single molecule" acting on all three [2].
The Zepbound label says tirzepatide binds and activates GIP and GLP-1 receptors. It adds that nonclinical studies suggest GIP may further help regulate food intake [12].
The glucagon part is the new idea. In preclinical models, retatrutide lowered food intake and raised energy expenditure, and its glucagon activity may reduce liver fat, according to researchers [7]. Those are animal findings, not proof in people.
In a phase 2a trial in humans, 86% of people on the 12 mg dose had normal liver fat after 24 weeks, vs 0% on placebo [7].
Is retatrutide a GLP-1? Yes, in part: it activates GLP-1 receptors along with two others. "GLP-3" is an online nickname for its three targets, not an official name or drug class.
Weight Loss: TRIUMPH-1 vs SURMOUNT-1
In people without diabetes, retatrutide's top dose led to more average weight loss than tirzepatide's top dose, in separate trials. On the efficacy estimand, TRIUMPH-1 reported 28.3% at 80 weeks and SURMOUNT-1 reported 22.5% at 72 weeks [1][9].
| Measure | Retatrutide 12 mg (TRIUMPH-1) | Tirzepatide 15 mg (SURMOUNT-1) |
|---|---|---|
| Trial length | 80 weeks | 72 weeks |
| Baseline BMI | 40.0 | 38.0 |
| Weight loss, efficacy estimand | 28.3% | 22.5% |
| Placebo, efficacy estimand | 2.2% | 2.4% |
| Difference vs placebo (our calculation) | 26.1 points | 20.1 points |
| Weight loss, treatment-regimen estimand | 25.0% | 20.9% |
| Placebo, treatment-regimen estimand | 3.9% | 3.1% |
| Difference vs placebo (our calculation) | 21.1 points | 17.8 points |
Sources: Lilly TRIUMPH-1 release (sponsor data, not yet in a journal), SURMOUNT-1 in NEJM and Lilly's 2022 release [1][8][9].
Why This Is Not a Head-to-Head Comparison
The two estimands answer different questions. The efficacy estimand estimates the result if everyone had stayed on the drug. The treatment-regimen estimand averages everyone, including people who stopped [1][9].
- Length. TRIUMPH-1 ran 80 weeks; SURMOUNT-1 ran 72.
- People. TRIUMPH-1 started at a higher average BMI (40.0 vs 38.0).
- Era. SURMOUNT-1 reported in 2022; TRIUMPH-1 reported in 2026.
The Zepbound label makes the same point about side effects: rates from one drug's trials "cannot be directly compared to rates in the clinical trials of another drug" [12]. It applies to weight results too.
Why Some Articles Still Say 24%
Older articles quote the 2023 phase 2 trial. It found 24.2% weight loss at 48 weeks on the 12 mg dose, vs 2.1% on placebo, in 338 adults [6].
Others quote 28.7%, calling it the biggest trial. That figure came from TRIUMPH-4, a 68-week trial of 445 people with knee osteoarthritis, not the largest study [5].
Retatrutide vs Tirzepatide in Type 2 Diabetes: TRIUMPH-2 and SURMOUNT-2
In retatrutide vs tirzepatide results for people with type 2 diabetes, retatrutide's top dose again led to more average weight loss in a separate trial. TRIUMPH-2 reported 20.8% at 80 weeks and SURMOUNT-2 15.7% at 72 weeks on the efficacy estimand, or 18.8% vs 14.7% on the treatment-regimen estimand [2][3][10][11].
| Measure | Retatrutide 12 mg (TRIUMPH-2) | Tirzepatide 15 mg (SURMOUNT-2) |
|---|---|---|
| Trial length | 80 weeks | 72 weeks |
| Baseline A1C | 7.7% | 8.02% |
| Weight loss, efficacy estimand | 20.8% | 15.7% |
| Placebo, efficacy estimand | 4.0% | 3.3% |
| Weight loss, treatment-regimen estimand | 18.8% | 14.7% |
| Placebo, treatment-regimen estimand | 5.1% | 3.2% |
Sources: Lilly TRIUMPH-2 release, September 29, 2026 (efficacy estimand), and the Lancet paper (treatment-regimen estimand); SURMOUNT-2 in The Lancet and Lilly's 2023 release [2][3][10][11].
TRIUMPH-2 also lowered blood sugar. A1C fell 1.5 points on 12 mg vs 0.2 on placebo, and 79.0% reached an A1C of 6.5% or lower, vs 26.3% [2].
Lilly presented the results at EASD in Milan (symposium on September 30, 2026), and The Lancet published the paper online at the same time [2][3]. Lilly's release gives efficacy-estimand values; the TRIUMPH-2 treatment-regimen values come from the paper's abstract [3].
TRIUMPH-5: The Head-to-Head Trial
TRIUMPH-5 is the phase 3 trial that compares retatrutide directly with tirzepatide. It is double-blind, has an estimated 800 adults with obesity, and measures percent weight change at week 80 [16].
Key facts from the registry [16]:
- Status. Active, not recruiting, as of September 30, 2026.
- Dates. Estimated primary completion November 2026; estimated completion December 2026. Lilly has not announced a date for results.
- Exclusions. Anyone who took weight-loss drugs, including over-the-counter ones, within 90 days before screening.
- Secondary outcomes. BMI, waist size, cholesterol, triglycerides, blood pressure, A1C, fasting insulin, and weight-related quality of life.
TRIUMPH-5 should show which drug causes more weight loss in one population over the same time. It will not show how switching works, because it excludes recent users of weight-loss drugs. A second trial, TRANSCEND-T2D-2, compares retatrutide with semaglutide in type 2 diabetes and has no results yet [17].
Stopping Rates and Side Effects in TRIUMPH-1 vs SURMOUNT-1
In retatrutide vs tirzepatide side effects data from separate trials, retatrutide's top dose had higher rates of nausea, vomiting, and dysesthesia, and more people stopped it. Each drug should be compared with its own placebo [1][12].
| Measure | Retatrutide 12 mg | TRIUMPH-1 placebo | Zepbound 15 mg | Zepbound placebo |
|---|---|---|---|---|
| Nausea | 42.4% | 14.8% | 28% | 8% |
| Vomiting | 25.3% | 4.8% | 13% | 2% |
| Dysesthesia | 12.5% | 0.9% | 0.4% | 0.1% |
| Stopped for adverse events | 11.3% | 4.9% | 6.2% | 2.6% |
Sources: Lilly TRIUMPH-1 release; Zepbound label trials, which pool SURMOUNT-1 and SURMOUNT-2 (nausea, vomiting, dysesthesia); SURMOUNT-1 (stopping) [1][8][12].
Dysesthesia, an unusual skin sensation, is the distinctive retatrutide signal: 12.5% vs 0.9% on placebo [1]. Other points:
- Stopping. 11.3% stopped retatrutide 12 mg for adverse events, vs 6.2% on tirzepatide 15 mg [1][8].
- Heart rate. Zepbound raised average heart rate by 1 to 3 beats per minute, per its label [12]. In phase 2, retatrutide's heart rate rise depended on dose, peaked at 24 weeks, then declined [6].
- Urinary tract infections. In TRIUMPH-1, 92% of UTIs occurred in female participants [20].
For diarrhea, constipation, and injection site reactions, see the full table in retatrutide side effects. For the full approved-drug picture, read Zepbound side effects.
Evidence Beyond Weight Loss
Tirzepatide has approved uses beyond weight, while retatrutide's heart data are still inconclusive. Mounjaro gained a cardiovascular risk-reduction approval in August 2026 [14].
Tirzepatide's approved uses:
- Weight (Zepbound), with obesity or overweight plus a related condition [12].
- Sleep apnea (Zepbound), moderate to severe, with obesity [12].
- Type 2 diabetes (Mounjaro), for blood sugar in adults and children 10 and older [14].
- Heart risk (Mounjaro), to lower major cardiovascular event risk in high-risk adults with type 2 diabetes [14].
SURPASS-CVOT supported that last use. In 13,165 people with type 2 diabetes and heart disease, tirzepatide was noninferior to dulaglutide: 12.2% vs 13.1% had a major event, hazard ratio 0.92 (0.83 to 1.01). Superiority was not shown [15].
For retatrutide, TRIUMPH-3 enrolled 1,949 people with heart disease. The hazard ratios were 1.12 (0.64 to 1.96) for MACE-3 and 0.82 (0.55 to 1.22) for MACE-5, with fewer events than expected [4]. These wide ranges include both benefit and harm. TRIUMPH-Outcomes, with about 10,000 people, has an estimated primary completion date of February 2029 [18].
Muscle, Protein, and Eating Well on Tirzepatide Now
Both retatrutide and tirzepatide cause loss of some lean mass along with fat, so protein and strength training matter now for anyone taking tirzepatide.
Does Retatrutide Burn Fat or Muscle?
Retatrutide cut fat mass sharply in one small study, with a lean-mass share like other treatments. In a 36-week phase 2 substudy of people with type 2 diabetes (103 with both scans), total fat mass fell 23.2% on 12 mg vs 4.5% on placebo [21]. The authors called the lean-mass share of weight lost "similar to other obesity treatments."
For tirzepatide, about a quarter of the weight lost in a SURMOUNT-1 substudy of 160 people was lean mass, the same share as placebo [22]. Both substudies come from Lilly-sponsored trials, and Lilly employees made up most or all of each author team. We found no retatrutide body-composition data beyond 36 weeks.
Protecting Muscle While You Take Tirzepatide
A 2025 joint nutrition advisory notes that protein targets of 1.2 to 1.6 grams per kilogram per day have been proposed during active weight loss [23]. The right body weight for that math is unsettled, and strength training is also needed.
Practical habits:
- Eat protein first at each meal, before you feel full.
- Keep easy protein on hand for low-appetite days, such as Greek yogurt, eggs, or cottage cheese.
- Do strength training regularly, as your clinician advises.
Our page on how much protein on GLP-1 explains the targets, and our GLP-1 meal plan shows a sample week. For high-protein recipes and meal ideas sized for a smaller appetite, see our guide.
Semaglutide, Tirzepatide, and Retatrutide Compared
Semaglutide acts on one receptor, tirzepatide on two, and retatrutide on three. Only semaglutide and tirzepatide are FDA approved, and they have head-to-head data against each other [24][25].
| Feature | Semaglutide | Tirzepatide | Retatrutide |
|---|---|---|---|
| Receptors | GLP-1 | GIP and GLP-1 | GIP, GLP-1, and glucagon |
| FDA status | Approved (for example, Wegovy) | Approved (Zepbound, Mounjaro) | Investigational |
| Head-to-head in obesity | SURMOUNT-5: 13.7% at 72 weeks | SURMOUNT-5: 20.2% at 72 weeks | TRIUMPH-5 vs tirzepatide, running |
| Head-to-head in type 2 diabetes | SURPASS-2 vs tirzepatide (semaglutide 1 mg) | SURPASS-2 vs semaglutide 1 mg | TRANSCEND-T2D-2 vs semaglutide, no results |
Sources: SURMOUNT-5 and SURPASS-2 in NEJM; ClinicalTrials.gov [16][17][24][25].
Our Zepbound vs Wegovy page covers the two approved brands, and the GLP-1 drugs list shows every approved option.
When Could Retatrutide Be Available? Filing Plan and Expanded Access
Retatrutide is not FDA approved as of September 30, 2026. Lilly plans to submit it to the FDA for approval in the first quarter of 2027, and no approval date has been announced [2].
Lilly states that retatrutide "cannot be legally sold or marketed for human use" [2]. It has no legal price.
Through physician-requested expanded access, a doctor can ask for retatrutide for one patient. The patient must be an adult with a BMI of 35 or more despite top-dose weight management therapy, two or more serious obesity-related complications, and no trial option [19].
FDA's warnings are direct [13]:
- Retatrutide cannot be used in compounding under federal law.
- FDA has warned companies that illegally sold retatrutide falsely labeled "for research purposes."
- FDA urges consumers not to buy these products, which are "of unknown quality and may be harmful."
A "retatrutide peptide" sold online is not the trial drug. Our compounded tirzepatide page explains the rules for the approved molecule. For tirzepatide costs and coverage, see Zepbound coupon and what insurance covers Zepbound.
Which Is Right for You Now?
Only tirzepatide can be prescribed today. Retatrutide is available only in trials or through expanded access [2][19].
Questions to bring to your prescriber:
- Which approved option fits my goals: weight, blood sugar, sleep apnea, or heart risk?
- Which side effects could I tolerate, and how would we manage them?
- Would a clinical trial fit my situation?
Retatrutide trials, with eligibility rules, are listed on ClinicalTrials.gov. Treatment choices belong to you and your prescriber.
Frequently Asked Questions
Is retatrutide better than tirzepatide?
Not proven, because no head-to-head result has been reported. In separate trials, retatrutide's top dose led to more weight loss, but more people stopped it for side effects. TRIUMPH-5 is testing the two directly.
Is retatrutide stronger than Mounjaro?
Mounjaro is tirzepatide, so the answer is the same, and no head-to-head result has been reported yet. Mounjaro is FDA approved for type 2 diabetes: blood sugar control and, since August 2026, lowering major cardiovascular event risk in high-risk adults. Retatrutide is not approved.
Can I switch from tirzepatide to retatrutide?
Only within a clinical trial or physician-requested expanded access, because retatrutide cannot be legally sold. We found no published switching protocol, and TRIUMPH-5 excluded anyone who took weight-loss drugs in the prior 90 days.
Can you take retatrutide and tirzepatide together?
The Zepbound label says using it with other tirzepatide products or any GLP-1 receptor agonist is not recommended, and retatrutide acts on GLP-1 receptors. We found no trial that tested the two together, and FDA warns against research-labeled retatrutide products.
Is retatrutide a GLP-1 or a GLP-3?
Retatrutide activates GLP-1 receptors, plus GIP and glucagon receptors. GLP-3 is an online nickname for its three targets, not an official name or drug class.
Is retatrutide peptide the same as the drug in the trials?
No. FDA says companies have illegally sold retatrutide falsely labeled for research, and it calls these products of unknown quality. The trial safety data apply only to the study drug.
When will retatrutide be available?
Lilly plans to submit retatrutide to the FDA in the first quarter of 2027. No approval date has been announced.
Key Takeaways
- One extra target. Retatrutide adds the glucagon receptor to tirzepatide's GIP and GLP-1 targets; the proposed glucagon effects come from animal studies.
- More weight loss in separate trials. Retatrutide vs tirzepatide top doses: 28.3% at 80 weeks vs 22.5% at 72 weeks on the efficacy estimand, not head to head.
- More stopping. 11.3% stopped retatrutide 12 mg for adverse events vs 6.2% on tirzepatide 15 mg.
- Direct answer pending. TRIUMPH-5 has an estimated primary completion of November 2026, with no results date announced.
- Only one is approved. Retatrutide is not approved and cannot be legally sold; "research" products are of unknown quality, per FDA.
References
- TRIUMPH-1 topline results, Lilly, May 21, 2026
- TRIUMPH-2 results at EASD and in The Lancet, Lilly, September 29, 2026
- Bellido V et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet, 2026, online September 29 (PMID 42810372)
- TRIUMPH-2 and TRIUMPH-3 topline results, Lilly, July 23, 2026
- TRIUMPH-4 topline results, Lilly, December 11, 2025
- Jastreboff AM et al. Retatrutide for obesity: a phase 2 trial. N Engl J Med, 2023
- Sanyal AJ et al. Retatrutide for steatotic liver disease: a phase 2a trial. Nat Med, 2024
- Jastreboff AM et al. Tirzepatide for the treatment of obesity (SURMOUNT-1). N Engl J Med, 2022
- SURMOUNT-1 topline results, Lilly, April 28, 2022
- Garvey WT et al. Tirzepatide for obesity in type 2 diabetes (SURMOUNT-2). Lancet, 2023
- SURMOUNT-2 topline results, Lilly, April 27, 2023
- Zepbound Prescribing Information, revised 08/2026
- FDA's concerns with unapproved GLP-1 drugs used for weight loss, current as of 09/01/2026
- Mounjaro Prescribing Information, revised 08/2026
- Nicholls SJ et al. Tirzepatide versus dulaglutide (SURPASS-CVOT). N Engl J Med, 2025
- TRIUMPH-5, NCT06662383, ClinicalTrials.gov
- TRANSCEND-T2D-2, NCT06260722, ClinicalTrials.gov
- TRIUMPH-Outcomes, NCT06383390, ClinicalTrials.gov
- Retatrutide expanded access, NCT07629401, ClinicalTrials.gov
- TRIUMPH-1 presentation, ADA 2026, Lilly information for health care professionals
- Coskun T et al. Retatrutide and body composition in type 2 diabetes. Lancet Diabetes Endocrinol, 2025
- Look M et al. Body composition with tirzepatide in SURMOUNT-1. Diabetes Obes Metab, 2025
- Nutritional priorities to support GLP-1 therapy: joint advisory (ACLM, ASN, OMA, TOS), 2025
- Aronne LJ et al. Tirzepatide vs semaglutide for obesity (SURMOUNT-5). N Engl J Med, 2025
- Frías JP et al. Tirzepatide vs semaglutide in type 2 diabetes (SURPASS-2). N Engl J Med, 2021
This article is for education only, is not medical advice, and gives no personalized dosing advice. Talk to your prescriber about your treatment. Read our full medical disclaimer.