Retatrutide vs Tirzepatide: Phase 3 Data Compared
Retatrutide is a triple agonist hitting GLP-1, GIP, and glucagon receptors. Tirzepatide is a dual agonist hitting GLP-1 and GIP. As of August 2026 retatrutide has Phase 3 results and tirzepatide has an FDA approval, which is the difference that actually matters for anyone making a treatment decision this year.
Status as of August 2026: Retatrutide is investigational. Topline Phase 3 TRIUMPH-1 results were announced May 21, 2026; TRIUMPH-2 and TRIUMPH-3 have not read out and no FDA submission has been announced. Tirzepatide is approved and marketed as Mounjaro (type 2 diabetes) and Zepbound (chronic weight management).
Head-to-Head Summary
Every efficacy comparison below is a cross-trial comparison. The two drugs have never been tested against each other in a randomized trial, so read the gap as an estimate with wide error bars rather than a measured result.
| Factor | Retatrutide | Tirzepatide |
|---|---|---|
| Receptor targets | GLP-1, GIP, glucagon (triple) | GLP-1, GIP (dual) |
| Regulatory status | Investigational, not approved | FDA approved (Mounjaro 2022, Zepbound 2023) |
| Best Phase 3 weight loss | 28.3% at 80 weeks (12 mg, TRIUMPH-1) | 20.9% at 72 weeks (15 mg, SURMOUNT-1) |
| Extended-duration data | 30.3% at 104 weeks (BMI 35+ subgroup, n=532) | Long-term data across the SURMOUNT program |
| Pivotal trial size | 2,339 (TRIUMPH-1) | 2,539 (SURMOUNT-1) |
| Nausea, top dose | 42.4% (12 mg) vs 14.8% placebo | Roughly 25-33% across doses |
| Discontinuation for AEs, top dose | 11.3% (12 mg) vs 4.9% placebo | Approximately 4-7% |
| Dosing | Once weekly subcutaneous, 2 mg start | Once weekly subcutaneous, 2.5 mg start |
| Can you get it today | No | Yes, with a prescription |
| Manufacturer | Eli Lilly | Eli Lilly |
For the dual-agonist side of this comparison in more depth, see tirzepatide dosage chart and tirzepatide vs semaglutide.
What TRIUMPH-1 Actually Showed
TRIUMPH-1 (NCT05929066) was a randomized, double-blind, placebo-controlled Phase 3 trial in 2,339 adults with obesity or overweight plus at least one weight-related comorbidity, excluding people with diabetes. Topline results were announced May 21, 2026. Mean baseline weight in the 12 mg arm was 248.5 lb at a BMI of 40.0.
- 4 mg: 47.2 lb mean loss, 19.0% of body weight at 80 weeks
- 9 mg: 64.4 lb mean loss, 25.9% at 80 weeks
- 12 mg: 70.3 lb mean loss, 28.3% at 80 weeks
- Responder rate: 45.3% of the 12 mg group lost 30% or more of body weight
- BMI normalization: 65.3% of the 12 mg group fell below a BMI of 30, including 37.5% of those who entered with class 3 obesity
- Waist circumference: 24.1 cm (9.5 inches) mean reduction on 12 mg
A prespecified blinded extension continued 532 participants with baseline BMI of 35 or higher out to 104 weeks at their maximum tolerated dose. Participants originally randomized to 12 mg reached 85.0 lb mean loss, 30.3% of a 268.3 lb baseline. That is the number quoted in most headlines, and it comes from a selected subgroup that tolerated treatment for two years, not from the full trial population.
Lilly said detailed data would be presented at the American Diabetes Association Scientific Sessions. Full peer-reviewed publication had not appeared as of this writing. Our dedicated breakdown is at retatrutide TRIUMPH-1 results.
What Changed Since the Phase 2 Data
For three years the number attached to retatrutide was 24.2%, from the 48-week Phase 2 trial published in the New England Journal of Medicine in 2023 (n=338). That trial was placebo-controlled. It did not include a tirzepatide arm, despite how often it gets described that way. Anyone presenting 24.2% versus 22% as a head-to-head result is repeating an error.
TRIUMPH-1 superseded that figure with a larger population and a longer treatment window. The 28.3% at 80 weeks is not directly comparable to 24.2% at 48 weeks either, since roughly eight additional months of titration and maintenance sit between them. Weight loss on this class continues to accumulate well past the one-year mark, which is most of why the numbers moved.
Triple vs Dual Agonism: The Mechanistic Argument
Tirzepatide activates two receptors. Retatrutide adds a third.
- GLP-1 receptor: suppresses appetite, slows gastric emptying, improves glucose-dependent insulin release
- GIP receptor: improves insulin sensitivity and appears to blunt the nausea burden of GLP-1 agonism at matched efficacy
- Glucagon receptor: raises resting energy expenditure and hepatic fat oxidation
The first two arms reduce how much you eat. The third increases how much you burn. That combination is the entire thesis behind triple agonism, and TRIUMPH-1 is the first large trial to test it properly. The glucagon arm is also why cardiovascular monitoring gets more attention with this molecule than with pure incretin drugs, since glucagon agonism can raise heart rate.
More detail: retatrutide mechanism of action.
Side Effects and Tolerability
TRIUMPH-1 adverse event rates by dose (4 mg, 9 mg, 12 mg) against placebo:
| Adverse event | 4 / 9 / 12 mg | Placebo |
|---|---|---|
| Nausea | 28.6% / 38.4% / 42.4% | 14.8% |
| Diarrhea | 25.2% / 34.1% / 32.0% | 13.5% |
| Constipation | 23.8% / 25.9% / 26.1% | 10.9% |
| Vomiting | 10.6% / 22.8% / 25.3% | 4.8% |
| Discontinued for AEs | 4.1% / 6.9% / 11.3% | 4.9% |
The pattern worth noticing: at 4 mg, discontinuation was lower than placebo. At 12 mg it was more than double. The extra 9.3 percentage points of weight loss between 4 mg and 12 mg cost a roughly threefold increase in dropout. That trade-off will drive real-world dosing if the drug is approved, and it mirrors what already happens with tirzepatide, where plenty of patients settle at 10 mg rather than push to 15 mg.
Other reported events included upper respiratory and urinary tract infections and mild to moderate dysesthesia, with most urinary and neurological cases resolving during continued treatment.
See also retatrutide side effects and Zepbound side effects.
Dosing Schedules
Both are once-weekly subcutaneous injections with a titration ramp designed to limit gastrointestinal side effects. Tirzepatide starts at 2.5 mg and steps up every four weeks to a maximum of 15 mg. Retatrutide in TRIUMPH-1 started at 2 mg, with the 4 mg arm requiring only one titration step and the 9 mg and 12 mg arms escalating further.
Reference charts: tirzepatide dosage chart, retatrutide dosage chart, retatrutide starting dose, and Zepbound doses.
Availability, Approval Timeline, and Cost
Tirzepatide is available now by prescription as Mounjaro for type 2 diabetes and Zepbound for chronic weight management. Retatrutide cannot be prescribed or dispensed anywhere.
Lilly has said additional Phase 3 readouts are expected during 2026, including TRIUMPH-2 in adults with obesity and type 2 diabetes and TRIUMPH-3 in adults with established cardiovascular disease. A new drug application would follow. There is no announced submission date and no PDUFA date, so any specific approval month circulating online is speculation.
Launch pricing is unknown. Current tirzepatide costs are the only reference point available and a weak one, given how much self-pay and direct-to-consumer pricing in this class has moved in the last two years. See tirzepatide cost and Zepbound cost for what is actually knowable today, and retatrutide FDA approval for timeline tracking.
On the gray market: vials sold online as research-use-only retatrutide sit outside the regulated supply chain with no verified identity, purity, sterility, or dose accuracy. Read retatrutide availability and research peptides before assuming what arrives in the mail is what the label says.
Where Retatrutide Sits Among Next-Generation Candidates
Retatrutide is not the only molecule chasing tirzepatide. Survodutide is a GLP-1/glucagon dual agonist. CagriSema pairs semaglutide with the amylin analog cagrilintide. Orforglipron is an oral small-molecule GLP-1 agonist, which matters less for peak efficacy than for how many people are willing to start treatment at all. Mazdutide is another GLP-1/glucagon agonist, furthest along in China.
Comparisons: survodutide vs tirzepatide, CagriSema vs tirzepatide, orforglipron vs tirzepatide, and mazdutide vs tirzepatide. Background on each: survodutide, cagrilintide, and orforglipron.
Practical Read
If you are choosing treatment in 2026, retatrutide is not on the menu. The comparison that matters right now is between the drugs a provider can actually prescribe, which means tirzepatide versus semaglutide. Retatrutide becomes relevant to your decision only if it is approved, priced, and stocked, and none of those has happened.
The one thing TRIUMPH-1 changes today is expectations. A 28.3% ceiling at 80 weeks in a triple agonist suggests the class has not plateaued, which is an argument against treating your current medication as a permanent choice.
Start here instead: semaglutide vs tirzepatide, Zepbound vs Mounjaro, and the GLP-1 guide. If you have seen the term GLP-3 used for retatrutide, read GLP-3 peptide for why that name is wrong. Broader class side effects: GLP-1 side effects.
Frequently Asked Questions
On weight loss alone, the Phase 3 numbers favor retatrutide. Retatrutide 12 mg produced 28.3% mean weight loss at 80 weeks in TRIUMPH-1. Tirzepatide 15 mg produced 20.9% at 72 weeks in SURMOUNT-1. But the trials ran at different durations in different populations and were never compared head to head, so the gap is an indirect estimate rather than a measured difference. Retatrutide also carried higher discontinuation for adverse events at its top dose (11.3% vs 4.9% on placebo), and it is not approved or prescribable. Tirzepatide is available today under two brand names.
No. There is no completed randomized trial that assigned patients to retatrutide or tirzepatide and measured both. The Phase 2 retatrutide trial published in the New England Journal of Medicine in 2023 was placebo-controlled, not tirzepatide-controlled. Every retatrutide-vs-tirzepatide number you see, including the ones on this page, is a cross-trial comparison. Cross-trial comparisons overstate differences when baseline weight, trial length, and titration schedules differ, and all three differ here.
Eli Lilly announced topline TRIUMPH-1 results on May 21, 2026. In 2,339 adults with obesity or overweight plus at least one weight-related comorbidity and no diabetes, mean weight loss at 80 weeks was 19.0% on 4 mg (47.2 lb), 25.9% on 9 mg (64.4 lb), and 28.3% on 12 mg (70.3 lb). In the 12 mg arm, 45.3% of participants lost 30% or more of body weight and 65.3% dropped below a BMI of 30. A prespecified 104-week extension in 532 participants with baseline BMI of 35 or higher reached 30.3% mean loss (85.0 lb) in the 12 mg arm.
It is not approved anywhere as of August 2026 and no FDA decision date exists yet. Lilly has said additional Phase 3 readouts, including TRIUMPH-2 in type 2 diabetes and TRIUMPH-3 in established cardiovascular disease, are expected during 2026. A new drug application would follow those readouts, and FDA review typically takes another 10 to 12 months after submission. Treat any specific approval date you see quoted online as speculation.
Not legally as a medication. Retatrutide is investigational, so no pharmacy can dispense it and no licensed provider can prescribe it. Vials sold online as research chemicals are outside the regulated supply chain, are not made under pharmaceutical manufacturing standards, and carry no verified identity, purity, sterility, or dose accuracy. Independent testing of gray-market peptides has repeatedly found underdosed, misidentified, and contaminated product.
The gastrointestinal profile is the same class of effects but the rates climb with dose. In TRIUMPH-1, nausea was reported by 28.6%, 38.4%, and 42.4% of the 4 mg, 9 mg, and 12 mg groups versus 14.8% on placebo. Vomiting was 10.6%, 22.8%, and 25.3% versus 4.8%. Discontinuation for adverse events was 4.1%, 6.9%, and 11.3% versus 4.9% on placebo, meaning the lowest dose was better tolerated than placebo while the top dose roughly doubled the placebo rate. Tirzepatide discontinuation for adverse events in SURMOUNT-1 ran in the 4% to 7% range across doses.
GLP-1 and GIP agonism mainly reduce energy intake through appetite suppression and slowed gastric emptying. Glucagon receptor agonism works on the other side of the equation by raising energy expenditure and increasing hepatic fat oxidation. Combining intake suppression with an expenditure increase is the mechanistic argument for why a triple agonist should outperform a dual agonist. The trade-off is that glucagon agonism can raise heart rate and, in isolation, raise glucose, which is why the molecule pairs it with two incretin arms.
Waiting has a real cost. Retatrutide has no approval date, two more Phase 3 readouts pending, and an unknown launch price. Tirzepatide is approved, available, and has years of post-market safety data. If a provider considers you a candidate for treatment now, the usual clinical reasoning is to treat now and reassess when new options are actually on the market. This is a decision for you and a licensed clinician, not one to make from a comparison table.
Unknown. Nobody outside Lilly has launch pricing, and US list prices for this class have been moving as direct-to-consumer programs and manufacturer self-pay channels expand. Anchoring to current tirzepatide pricing is the only available reference point, and it is a weak one. Any figure quoted today for retatrutide is a guess.
No. There is no hormone or drug class called GLP-3. The term circulates in peptide forums and gray-market listings as shorthand for retatrutide, apparently on the logic that a triple agonist is one better than a dual agonist. It has no basis in pharmacology.
Informational only, not medical advice. Retatrutide is an investigational drug not approved by the FDA or any other regulator as of August 2026 and cannot be legally prescribed or dispensed. TRIUMPH-1 figures are from Eli Lilly's topline announcement of May 21, 2026; full peer-reviewed results had not published as of this writing and numbers may be revised. Tirzepatide comparisons are cross-trial, not head-to-head. Talk to a licensed clinician about treatment decisions.