Retatrutide vs Tirzepatide: Trial Data, Approval Status and Cost Compared (2026)
Quick answer: Retatrutide (LY3437943) is investigational and not FDA-approved. Tirzepatide (Mounjaro, Zepbound) is an FDA-approved prescription drug. Published trials report large average weight changes on both, but those trials enrolled different people for different lengths of time, and no head-to-head result exists yet. The retatrutide vs tirzepatide trial, TRIUMPH-5, had no posted results as of October 2, 2026. This page compares what the trials reported and does not recommend either drug.
Key takeaways
- Status: tirzepatide has been FDA-approved since May 2022 (Mounjaro) and November 2023 (Zepbound). Retatrutide is still in Phase 3, and Lilly says it plans to submit a Biologics License Application in the first quarter of 2027.
- No head-to-head result: TRIUMPH-5 (NCT06662383) randomizes about 800 adults with obesity to retatrutide or tirzepatide, with weight change at week 80 as the primary outcome. ClinicalTrials.gov estimates primary completion in November 2026.
- Weight data come from separate trials. TRIUMPH-1 reported -25.0% for retatrutide 12 mg at 80 weeks (placebo -3.9%). SURMOUNT-1 reported -20.9% for tirzepatide 15 mg at 72 weeks (placebo -3.1%). These are not head-to-head figures.
- Zepbound has published prices: about $1,088 per month before the 2026 TrumpRx reduction, and $299 to $449 per month under Lilly’s current self-pay offer terms. Retatrutide has no price. The $1,000 to $1,500 per month that two clinic sites project is not an announced price.
For laboratory and research use only. Nothing here is medical advice. Talk to a licensed clinician about any approved medication.
Retatrutide vs Tirzepatide at a Glance
Eli Lilly developed both compounds, and both act on more than one hormone receptor. In a retatrutide peptide vs tirzepatide comparison, the biggest difference is regulatory status. The table reflects what was published as of October 2, 2026.
| Retatrutide | Tirzepatide | |
|---|---|---|
| Developer | Eli Lilly (code LY3437943) | Eli Lilly (code LY3298176) |
| FDA status | Investigational, not approved | Approved prescription drug |
| Brand names | None | Mounjaro (type 2 diabetes), Zepbound (weight management, sleep apnea) |
| Receptors targeted | GIP, GLP-1 and glucagon | GIP and GLP-1 |
| Stage of evidence | Phase 3. Lilly has reported results from TRIUMPH-1 through TRIUMPH-4 between December 2025 and September 2026. | Marketed, with completed Phase 3 programs (SURMOUNT) |
| Head-to-head against the other | TRIUMPH-5 is running, no results | None reported |
| Public availability | No approved product. Pre-approval access is limited and controlled by Lilly (see below). | Prescription only |
Lilly’s Q2 2026 earnings release repeats the Q1 2027 filing plan, and no submission had been announced by October 2. Our retatrutide FDA approval status page tracks the timeline.
On pre-approval access, Lilly said it believes it is medically appropriate to make retatrutide available before FDA approval to a limited number of patients who meet specific medical criteria and cannot enroll in a clinical trial, and that it is reviewing provider requests (STAT, August 2026). That is a sponsor-controlled process. Research suppliers, including Peptryn, are not part of it, and research material is not a route to it.
The weight-loss and side-effect figures below name their trial. Peptryn lists retatrutide, tirzepatide and semaglutide only as laboratory research materials for research use only, and it does not sell any of them as a medicine.
How Retatrutide and Tirzepatide Work
All three drugs in this comparison mimic natural hormones that regulate appetite and blood sugar. They differ in how many receptors they act on.
Semaglutide (Ozempic, Wegovy) activates the GLP-1 receptor. Tirzepatide adds the GIP receptor, and the Zepbound label says it binds to and activates both the GIP and GLP-1 receptors. Retatrutide adds a third target, the glucagon receptor, and Lilly describes it as a single molecule that activates all three. Lilly’s chief scientific and medical officer said in 2023 that adding glucagon receptor activity may be one reason for the Phase 2 weight reduction. That is a hypothesis from the sponsor, and the sources reviewed for this article do not separate how much each receptor contributes.
| Compound | Receptors activated | US status |
|---|---|---|
| Semaglutide | GLP-1 | Approved |
| Tirzepatide | GIP, GLP-1 | Approved |
| Retatrutide | GIP, GLP-1, glucagon | Investigational |
How long each molecule stays in circulation is a separate question, covered on the retatrutide half-life page.
Retatrutide vs Tirzepatide Weight Loss Comparison: What Each Trial Reported
The table lists what each named trial measured in its own participants. Tirzepatide is FDA-approved to reduce excess body weight in adults with obesity, or overweight with a weight-related condition. Retatrutide is not approved for any use.
These are different trials with different populations, durations and designs. The figures are not a head-to-head comparison, and no trial in the table compared retatrutide with tirzepatide.
| Trial | Population | Duration | Dose arms | Mean weight change |
|---|---|---|---|---|
| Retatrutide Phase 2 (NEJM 2023) | 338 adults, BMI 30 or higher, or 27 to under 30 with a weight-related condition | 48 weeks | 1, 4, 8, 12 mg | -8.7%, -17.1%, -22.8%, -24.2% (placebo -2.1%) |
| TRIUMPH-1 (NEJM 2026) | 2,339 adults without diabetes, BMI 30 or higher, or 27 or higher with a weight-related condition | 80 weeks | 4, 9, 12 mg | -17.6%, -23.7%, -25.0% (placebo -3.9%) |
| TRIUMPH-201861-1) (Lancet 2026) | 1,152 adults with type 2 diabetes and obesity or overweight | 80 weeks | 4, 9, 12 mg | -11.9%, -16.8%, -18.8% (placebo -5.1%) |
| TRIUMPH-3 (Lilly release, July 2026) | 1,949 adults, BMI 35 or higher with cardiovascular disease, with or without type 2 diabetes | 80 weeks | 9, 12 mg | -21.6%, -22.6% (placebo -3.2%), efficacy estimand |
| TRIUMPH-4 (Lilly release, December 2025) | 445 adults with obesity or overweight and knee osteoarthritis | 68 weeks | 9, 12 mg | -20.0%, -23.7% (placebo -4.6%), treatment-regimen estimand |
| SURMOUNT-1 (NEJM 2022) | 2,539 adults, BMI 30 or higher, or 27 or higher with a weight-related complication, no diabetes | 72 weeks | Tirzepatide 5, 10, 15 mg | -15.0%, -19.5%, -20.9% (placebo -3.1%) |
Estimand key: treatment-regimen counts every randomized participant. Efficacy estimates the effect had all participants stayed on treatment, and it gives larger figures.
The TRIUMPH-1, TRIUMPH-2 and SURMOUNT-1 rows use the treatment-regimen estimand, which counts every randomized participant whether or not they stayed on treatment. The Phase 2 figures are least-squares means from the NEJM paper (its 4 mg and 8 mg figures each combine subgroups that started at 2 mg or 4 mg), and the TRIUMPH-3 and TRIUMPH-4 rows name the estimand Lilly used. Lilly’s headline numbers often use the efficacy estimand instead: 28.3% for TRIUMPH-1 12 mg at 80 weeks (Lilly, June 2026) and 22.5% for SURMOUNT-1 tirzepatide 15 mg at 72 weeks, against 2.4% for placebo (Lilly release). These come from separate trials and are not a head-to-head comparison. Check which estimand a figure uses before reading any number.
Even with matching estimands, separate trials differ in baseline weight (104.8 kg in SURMOUNT-1, 106.4 kg in TRIUMPH-2, 111.4 kg in TRIUMPH-3), population, length and dose arms. Eli Lilly funded all of them, and the TRIUMPH-3 and TRIUMPH-4 rows rest on Lilly press releases. The Phase 2 trial’s primary endpoint was week 24 (12 mg: -17.5% against -1.6% for placebo), so its 48-week numbers are secondary results.
Has Retatrutide Been Tested Head-to-Head Against Tirzepatide?
Not with a reported result. Lilly has registered one randomized comparison, TRIUMPH-5, and it is still running. This is what the ClinicalTrials.gov record shows (checked October 2, 2026):
| Item | TRIUMPH-5 (NCT06662383) |
|---|---|
| Design | Phase 3, randomized, double-blind |
| Comparison | Retatrutide vs tirzepatide (active comparator) |
| Population | Adults with obesity |
| Estimated enrollment | 800 |
| Primary outcome | Percent change in body weight, baseline to week 80 |
| Start | November 1, 2024 |
| Primary completion | November 2026 (estimated) |
| Status | Active, not recruiting; no results posted |
Lilly has not announced a readout date. Its releases through September 2026 and its Q2 2026 earnings release mention no TRIUMPH-5 results. Registry dates are estimates: ClinicalTrials.gov lists primary completion in November 2026 and study completion in December 2026, and neither is a Lilly readout date.
A head-to-head result would put both drugs in one trial, one population and one 80-week window, analyzed the same way. That gives one clean between-drug difference in weight change, plus adverse events and discontinuations under a single protocol. It would still describe one population and one time frame, and it would say little about cost or about people outside the trial.
SURMOUNT-5 shows what such a report looks like. This phase 3b, open-label, Lilly-funded trial randomized 751 adults with obesity and no type 2 diabetes to tirzepatide or semaglutide for 72 weeks (NEJM 2025). Weight change at week 72 was -20.2% with tirzepatide and -13.7% with semaglutide. Until TRIUMPH-5 reports, any retatrutide vs tirzepatide weight loss comparison puts results from separate trials next to each other, and those cannot say which drug is better.
Retatrutide vs Tirzepatide: Which Is Better?
This page cannot say which is better for any person. Tirzepatide is an approved prescription drug with a prescribing label and real-world use dating to 2022. Retatrutide is investigational, and its trial results are still being reported. Whether either suits an individual depends on medical history, goals and the judgment of the treating clinician. Trial averages describe the people enrolled, and an individual’s result can differ.
| Question | Retatrutide | Tirzepatide |
|---|---|---|
| Prescribing label | None. Safety information comes from trial reports and Lilly releases. | Yes. The Zepbound label carries a boxed warning for thyroid C-cell tumors seen in rats, with human relevance unknown. |
| Time on the market | Not on the market | Since May 2022 (Mounjaro) |
The retatrutide obesity trials so far compare it with placebo, so they say nothing direct about tirzepatide. The evidence does not yet include:
- A head-to-head result. TRIUMPH-5 is the registered trial, and Lilly has given no results date.
- Regulatory approval. No Biologics License Application had been announced as of early October 2026.
- Post-approval safety data for retatrutide. That kind of data builds up once a drug is on the market, and retatrutide is not.
This page does not recommend either drug or a switch from one to the other.
Side Effects Reported in the Trials
Adverse event rates from different trials are not directly comparable, because populations, durations, doses and event recording differ.
The Phase 2 retatrutide trial called gastrointestinal events the most common adverse events and described them as dose-related, with dose-dependent heart-rate increases that peaked at 24 weeks and then declined. Dysesthesia, an altered skin sensation, appears in the Phase 3 reports at higher rates than on placebo. In the table below, rates are percent of participants on the top studied dose versus placebo.
| Trial | Arm | Nausea | Vomiting | Dysesthesia | Stopped for adverse events |
|---|---|---|---|---|---|
| TRIUMPH-1 (80 weeks, 2,339 adults, Lilly release) | Retatrutide 12 mg | 42.4 vs 14.8 | 25.3 vs 4.8 | 12.5 vs 0.9 | 11.3 vs 4.9 |
| TRIUMPH-4 (68 weeks, 445 adults, Lilly release) | Retatrutide 12 mg | 43.2 vs 10.7 | 20.9 vs 0.0 | 20.9 vs 0.7 | 18.2 vs 4.0 |
| TRIUMPH-2 (80 weeks, 1,152 adults with type 2 diabetes, Lilly release) | Retatrutide 12 mg | 28.0 vs 8.0 | 15.7 vs 4.2 | 7.3 vs 0.7 | 7.7 vs 4.9 |
Lilly called the TRIUMPH-4 dysesthesia events generally mild and said they rarely led to discontinuation. It said adverse-event discontinuation rates in that trial were highly correlated with baseline BMI and included stops for perceived excessive weight loss.
For context, these figures come from separate trials and are not comparable with the retatrutide numbers above. SURMOUNT-1 (tirzepatide, 72 weeks, 2,539 adults) listed gastrointestinal events as most common, mostly mild to moderate and mainly during dose escalation. Adverse events led to discontinuation in 4.3%, 7.1% and 6.2% on 5, 10 and 15 mg, against 2.6% on placebo. STEP 1 (semaglutide 2.4 mg, 68 weeks, 1,961 adults) reported nausea and diarrhea as most common, with gastrointestinal discontinuation in 4.5% against 0.8% on placebo. In SURMOUNT-5, Lilly’s release gives discontinuation from adverse events of 6.1% on tirzepatide and 8.0% on semaglutide.
No trial yet reports retatrutide adverse events against tirzepatide. The TRIUMPH-1, TRIUMPH-2 and TRIUMPH-4 rates above come from Lilly press releases.
Semaglutide vs Tirzepatide vs Retatrutide
For readers searching all three, the table gives each drug’s receptors, status and one headline trial. Semaglutide and tirzepatide are approved prescription drugs. Retatrutide is investigational.
| Drug | Receptors | FDA status | Headline trial (top dose vs placebo) |
|---|---|---|---|
| Semaglutide | GLP-1 | Approved (Ozempic, December 2017; Wegovy, June 2021) | STEP 1 (NEJM 2021): 2.4 mg, 68 weeks, -14.9% vs -2.4% |
| Tirzepatide | GIP, GLP-1 | Approved (Mounjaro, May 2022; Zepbound, November 2023) | SURMOUNT-1 (NEJM 2022): 15 mg, 72 weeks, -20.9% vs -3.1% |
| Retatrutide | GIP, GLP-1, glucagon | Investigational | TRIUMPH-1 (NEJM 2026): 12 mg, 80 weeks, -25.0% vs -3.9% |
These figures come from three different trials and are not a head-to-head comparison. STEP 1 enrolled 1,961 adults with obesity or overweight and no diabetes, SURMOUNT-1 enrolled 2,539 adults without diabetes, and TRIUMPH-1 enrolled 2,339 adults without diabetes. STEP 1 was funded by Novo Nordisk, and SURMOUNT-1 and TRIUMPH-1 by Lilly. The doses and durations differ. The SURMOUNT-1 and TRIUMPH-1 rows use the treatment-regimen estimand, and the STEP 1 figures are as reported in its NEJM abstract.
SURMOUNT-5 is the head-to-head trial of tirzepatide against semaglutide, described above. It tested semaglutide at 1.7 or 2.4 mg. Retatrutide has no head-to-head result against either drug yet. Another retatrutide comparison is on our cagrilintide vs retatrutide page.
Retatrutide vs Tirzepatide Cost
Tirzepatide and semaglutide have published prices because both are FDA-approved prescription drugs. Prices below were checked October 2, 2026, except where a source date is given.
Zepbound, the tirzepatide product labeled for weight management, was priced at about $1,088 per month before the 2026 TrumpRx reduction, according to the White House fact sheet (February 2026). Third-party sources cite slightly different list figures, such as about $1,060 from Maryland Trim Clinic. Lilly’s self-pay prices run from $299 per month for the lowest strength to $449 per month for the higher strengths under current offer terms, and the page lists regular prices up to $699 for the highest strengths. Wegovy, the semaglutide product for weight management, has a list price of $1,349.02 per package. Insurance coverage for weight-loss use varies by plan and employer.
Retatrutide has no approved price because it is not approved, and none of the Lilly releases reviewed for this article states one. Two clinic websites project roughly $1,000 to $1,500 per month if it is approved. Maryland Trim Clinic (April 2026) bases that on Wegovy at about $1,350 and Zepbound at about $1,060, and InCareNow (September 2026) gives the same range as an analyst-based estimate. Maryland Trim Clinic says no official price has been announced and that analysts anticipate a similar range, and InCareNow calls the range speculation. Neither figure is an announced price.
Peptryn sells retatrutide as a laboratory research material, research use only, 21+, not for human or animal use, in 10mg, 30mg and 60mg vials. Research material and prescription medicine are different product categories, so their prices are not comparable. Our retatrutide research material pricing guide lists the vial prices, the per-mg breakdown and a vendor comparison.
| Item | Category | Price point | Source |
|---|---|---|---|
| Zepbound (tirzepatide) | Approved prescription, price before TrumpRx reduction | About $1,088 per month | White House fact sheet, Feb 2026 |
| Zepbound (tirzepatide) | Approved prescription, manufacturer self-pay | $299 to $449 per month by strength, offer terms apply (regular prices up to $699) | zepbound.lilly.com |
| Wegovy (semaglutide) | Approved prescription, list price | $1,349.02 per package | NovoCare |
| Retatrutide | Investigational | No price announced | None in the Lilly releases reviewed |
| Retatrutide | Outside projection, not confirmed | Roughly $1,000 to $1,500 per month if approved | Maryland Trim Clinic; InCareNow |
Sourcing Retatrutide for Research?
Lyophilized, tested by MZ Biolabs, free shipping over $150, same-day dispatch from the USA. Research use only, 21+.
Retatrutide Peptide for Research: What to Check Before You Buy
This section is for readers sourcing retatrutide for laboratory work. Peptryn sells it only as a lyophilized (freeze-dried) research material, for research use only, 21+, not for human or animal use. Retatrutide is not approved by the FDA, and a research vial is not a substitute for any approved medication.
A retatrutide listing should let you check five things before you order:
- A lot-specific certificate of analysis (COA). The certificate should carry a lot number and test date that match your vial. One generic PDF reused across lots tells you nothing about your lot. See what a COA is.
- A named independent lab. Peptryn’s reports come from MZ Biolabs. A named lab gives you someone to ask about the report.
- Purity by HPLC (a chromatography test that measures purity). Look for a percentage and a stated method. Peptide purity covers what the figure means.
- Identity by mass spectrometry. The mass should match retatrutide’s molecular weight of about 4,731 daltons (Da; CAS 2381089-83-2). A purity percentage alone does not say which compound was measured.
- An endotoxin result. It should appear on the report as a stated result.
Peptryn’s current listings and lot reports:
| Vial | Price | Per mg | Lot | Purity (HPLC) | Headline result on product page |
|---|---|---|---|---|---|
| 10mg | $130.00 | $13.00 | 2026-06-12 | 99.62% | Endotoxin negative |
| 30mg | $225.00 | $7.50 | 2026-08-31 | 99.32% | Identity confirmed by mass spectrometry |
| 60mg | $320.00 | $5.33 | On request | On request | Report on request |
MZ Biolabs tested the 10mg and 30mg lots. The table carries headline results only. The full reports are on the 10mg COA page and the 30mg COA page. A 60mg report goes out by email on request ([email protected]). Read the full reports for every test run on a lot.
Orders over $150 ship free, with same-day dispatch from the USA. Our vendor verification checklist applies these checks to any supplier, and our research sourcing guide covers the process for laboratory buyers. All Peptryn research material is for research use only, not for human or animal use. For the legal side, see are peptides legal.
Retatrutide Research Vials
Lyophilized, tested by MZ Biolabs, free shipping over $150, same-day dispatch from the USA. Research use only, 21+.
FAQ
Is retatrutide better than tirzepatide?
This page cannot say which is better for any person. Tirzepatide is an FDA-approved prescription drug with a prescribing label. Retatrutide is investigational, and its trial results are still being reported. No head-to-head result has been published. TRIUMPH-5 compares the two in adults with obesity, with an estimated primary completion of November 2026. Whether either drug suits an individual depends on medical history and the treating clinician, and this page does not recommend either one.
How much weight did people lose on retatrutide versus tirzepatide in trials?
Separate trials studied the two drugs, so these figures are not a head-to-head comparison. In TRIUMPH-1 (2,339 adults with obesity and no diabetes, 80 weeks), the retatrutide 12 mg arm averaged -25.0% against -3.9% on placebo under the treatment-regimen estimand. In SURMOUNT-1 (2,539 adults without diabetes, 72 weeks), the tirzepatide 15 mg arm averaged -20.9% against -3.1% on placebo under the same estimand. The trials differ in population, duration, dose arms and baseline weight.
Has retatrutide been compared directly with tirzepatide?
Not with a reported result. TRIUMPH-5 (NCT06662383) is a Phase 3, randomized, double-blind trial of retatrutide against tirzepatide in an estimated 800 adults with obesity. Its primary outcome is percent change in body weight at week 80. ClinicalTrials.gov lists primary completion as estimated November 2026 and no posted results.
How does retatrutide cost compare with tirzepatide?
Retatrutide has no approved price because it is not approved. Two clinic websites project roughly $1,000 to $1,500 per month if it is approved, and that range is not an announced price. Zepbound was priced at about $1,088 per month before the 2026 TrumpRx reduction, and Lilly’s self-pay prices run $299 to $449 per month under current offer terms (regular prices go up to $699). Research material is a different product category from a prescription medicine, so its prices are not comparable. See the research material pricing guide for vial pricing.
Is retatrutide FDA approved?
No. Retatrutide is investigational. Lilly says it plans to submit a Biologics License Application in the first quarter of 2027, and no submission had been announced as of October 2, 2026. See the FDA approval status page.
Can you switch from tirzepatide to retatrutide?
No approved retatrutide product exists to switch to. This page gives no guidance on switching medicines. Decisions about prescription drugs such as Mounjaro and Zepbound belong with a licensed clinician who knows the patient’s history and current medications.
What is the difference between semaglutide, tirzepatide and retatrutide?
They differ in receptor targets and regulatory status. Semaglutide (Ozempic, Wegovy) activates the GLP-1 receptor. Tirzepatide (Mounjaro, Zepbound) activates the GIP and GLP-1 receptors. Retatrutide activates GIP, GLP-1 and glucagon receptors. The first two are FDA-approved, and retatrutide is investigational. The one completed head-to-head trial among them, SURMOUNT-5, compared tirzepatide with semaglutide, was open-label and Lilly-funded, and reported -20.2% against -13.7% at week 72.
Do “retatrutide peptide” and “retatrutide” mean the same thing?
Yes. Both refer to retatrutide (LY3437943), with a molecular weight of about 4,731 Da and CAS number 2381089-83-2. Research suppliers such as Peptryn offer it as lyophilized laboratory material for research use only, 21+. Peptryn’s lot reports, tested by MZ Biolabs, are on the 10mg COA page and the 30mg COA page.
Related: Eloralintide vs retatrutide, tirzepatide and semaglutide · What is eloralintide?
Sources
- Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a Phase 2 trial. NEJM 2023.
- Retatrutide for treatment of obesity (TRIUMPH-1). NEJM, September 29, 2026.
- Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2).01861-1) The Lancet, 2026.
- Lilly press releases: TRIUMPH-4, December 11, 2025; TRIUMPH-1, June 6, 2026; TRIUMPH-2 and TRIUMPH-3, July 23, 2026; TRIUMPH-2 full results, September 29, 2026.
- Lilly Phase 2 retatrutide release (2023).
- ClinicalTrials.gov: TRIUMPH-5 (NCT06662383).
- Eli Lilly Q2 2026 earnings release (SEC Form 8-K), August 5, 2026.
- STAT: Lilly retatrutide pre-approval access, August 3, 2026.
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). NEJM 2022. Lilly SURMOUNT-1 release (efficacy estimand figures).
- Aronne LJ et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). NEJM 2025. Lilly SURMOUNT-5 release.
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM 2021.
- FDA prescribing information: Zepbound, revised August 2026; Wegovy, revised March 2026.
- White House fact sheet: TrumpRx.gov, February 2026.
- Zepbound savings and insurance options (zepbound.lilly.com). Wegovy cost and savings (NovoCare).
- Maryland Trim Clinic: Retatrutide cost, status and timeline. InCareNow: 4 facts about retatrutide prescription cost in 2026.
- Peptryn, retatrutide product page and published Certificates of Analysis, MZ Biolabs.
