Retatrutide in 2026: What the Phase 3 TRIUMPH Data Actually Showed
The triple agonist posted 28.3% mean weight reduction at 80 weeks and 30.3% at 104 weeks. Here are the real numbers from TRIUMPH-1, -2 and -3, how they compare to tirzepatide and semaglutide, and what the data does not say.
- Retatrutide (GLP-3/RT, trial code LY3437943) is a triple-hormone-receptor agonist acting on GIP, GLP-1 and glucagon receptors — semaglutide targets one, tirzepatide two.
- TRIUMPH-1, the pivotal Phase 3 obesity trial (2,339 participants, reported May 21, 2026), showed 28.3% mean body-weight reduction at 80 weeks on 12 mg versus 2.2% on placebo.
- A 104-week extension in participants with BMI 35 or above reached 30.3% mean reduction — an average of 85 lb (38.6 kg).
- 45.3% of participants on 12 mg lost at least 30% of body weight, against 0.5% on placebo; 65.3% finished with a BMI below 30.
- Retatrutide is not approved by any regulator. Lilly has stated it plans to file a Biologics License Application with the FDA in Q1 2027.
- Gastrointestinal effects dominated: nausea 42.4% and diarrhea 32.0% at 12 mg, with 11.3% discontinuing due to adverse events versus 4.9% on placebo.
- Supplied for in vitro laboratory research use only — not approved by Health Canada for therapeutic use and not for human or veterinary consumption.
The compound that made everyone recalculate
For two years the obesity-research conversation had a ceiling, and tirzepatide was it. Then the retatrutide numbers landed and the ceiling moved.
Retatrutide — listed in this catalogue as GLP-3/RT, and known in the literature as LY3437943 — is what pharmacologists call a triple agonist. Semaglutide (Ozempic, Wegovy) engages one receptor: GLP-1. Tirzepatide (Mounjaro, Zepbound) engages two: GIP and GLP-1. Retatrutide engages three, adding the glucagon receptor.
That third receptor is the interesting one, and it is counterintuitive. Glucagon is the hormone that raises blood sugar — the physiological opposite of insulin. Agonising it sounds like the last thing a metabolic compound should do. But glucagon-receptor activity also increases energy expenditure and drives hepatic fat mobilisation. The design bet was that pairing it with two incretin agonists would let the incretin arms handle glycemic control while the glucagon arm turned up energy burn.
The trial data suggests the bet paid off.
What TRIUMPH-1 measured
TRIUMPH-1 is the pivotal Phase 3 obesity trial. Topline results were released May 21, 2026: 2,339 participants randomised 1:1:1:1 to 4 mg, 9 mg, 12 mg or placebo, with the primary endpoint at 80 weeks.
| Arm | Mean weight reduction at 80 weeks | Average loss |
|---|---|---|
| Placebo | 2.2% | 5.5 lb (2.5 kg) |
| 4 mg | 19.0% | 47.2 lb (21.4 kg) |
| 9 mg | 25.9% | 64.4 lb (29.2 kg) |
| 12 mg | 28.3% | 70.3 lb (31.9 kg) |
The secondary endpoints are where it gets unusual. At 12 mg, 45.3% of participants lost at least 30% of their body weight — a threshold that barely existed in pharmacological obesity research before this compound. The placebo figure was 0.5%. Some 65.3% of participants on 12 mg finished with a BMI below 30, meaning they were no longer classified as obese. Mean waist-circumference reduction at 12 mg was 9.5 inches (24 cm).
A 104-week extension followed 532 participants with baseline BMI of 35 or above. Those on the maximum tolerated dose reached 30.3% mean weight reduction — an average of 85 lb (38.6 kg).
TRIUMPH-2 and TRIUMPH-3
Lilly reported two further Phase 3 trials on July 23, 2026.
TRIUMPH-2 enrolled 1,152 adults with type 2 diabetes and obesity or overweight over 80 weeks. Weight reduction reached 20.8% at 12 mg versus 4.0% on placebo — lower than TRIUMPH-1, which is the expected pattern in a diabetic population. A1C fell by up to 1.6 percentage points against 0.2 for placebo.
TRIUMPH-3 enrolled 1,949 adults with severe obesity and established cardiovascular disease. At 12 mg, mean weight reduction was 22.6% (55.8 lb / 25.3 kg) versus 3.2% on placebo.
Together the three trials cover more than 5,400 randomised participants across populations most obesity programmes study separately.
Retatrutide vs tirzepatide vs semaglutide
The comparison everyone runs — with the caveat that matters. These figures come from separate trials with different populations, durations and designs. Cross-trial comparison is directional, not definitive. Only a head-to-head trial settles it, and none has reported.
| Compound | Receptors | Peak trial weight reduction |
|---|---|---|
| Semaglutide | GLP-1 | 14.9% (STEP-1, 68 weeks, n=1,961) |
| Tirzepatide | GIP + GLP-1 | 22.5% (SURMOUNT-1, 72 weeks, n=2,539) |
| Retatrutide | GIP + GLP-1 + glucagon | 28.3% (TRIUMPH-1, 80 weeks, n=2,339) |
The pattern that stands out is dose-response steepness. In the earlier Phase 2 trial — 338 participants, published in the New England Journal of Medicine on June 26, 2023 by Jastreboff and colleagues — the 48-week curve had still not clearly plateaued at the top dose: minus 8.7% at 1 mg, minus 17.1% at 4 mg, minus 22.8% at 8 mg and minus 24.2% at 12 mg, against minus 2.1% for placebo. A compound whose highest dose has not flattened by 48 weeks is unusual, and it is a large part of why the longer 80-week and 104-week readouts drew the attention they did.
For a compound-level comparison against the dual agonist, see our GLP-2/Tirz vs GLP-3/RT researcher comparison.
What the data does not say
Any honest summary needs this section, and most pages competing for this search term skip it.
Retatrutide is not approved by any regulator — not the FDA, not Health Canada, not the EMA. Lilly has stated it plans to submit a Biologics License Application to the FDA in Q1 2027. A submission date is not an approval date, and approval is not guaranteed.
The tolerability profile is real. At 12 mg in TRIUMPH-1: nausea in 42.4% of participants against 14.8% on placebo, diarrhea in 32.0% against 13.5%, and 11.3% discontinuing because of adverse events versus 4.9%. Roughly one in nine people at the top dose stopped taking it. In the Phase 2 trial, gastrointestinal effects were the most common adverse events and were described as mild-to-moderate.
Long-term safety is unresolved. The longest published follow-up is 104 weeks in a subgroup. The glucagon-receptor arm — the mechanism that makes retatrutide distinctive — is also the least clinically characterised of the three, and questions around heart rate and hepatic effects remain open in the literature.
Everything above describes supervised clinical trials with dose titration, monitoring and clinicians managing adverse events. It does not describe anything else.
Sourcing GLP-3/RT in Canada
Because retatrutide is unapproved, there is no pharmacy supply chain and no regulator standing behind what is in the vial. That makes the supplier the entire quality-control system, which is why sourcing matters more here than for almost any other compound in a research catalogue.
Popular Peptides supplies GLP-3/RT for laboratory research use. Concretely:
- —**It ships from within Canada.** From Vancouver, BC, typically 2 to 5 business days, tracked and insured. No customs clearance, no border seizure, no three-week silence wondering whether a package cleared. Most research compounds bought in Canada arrive from overseas and take that risk on every order. Ours do not cross a border.
- —**Every batch is independently tested.** HPLC for purity, LC-MS for identity, by a third-party lab rather than by us. Published-batch HPLC purity has averaged above 99%. You can look up any lot number and read the certificate of analysis yourself — measured purity, methods, analysis date, result. Not a badge on a product page: the actual document, matched to the vial in your hand. Browse all published lab results if you would rather see the full set first.
- —**Priced and charged in Canadian dollars,** with card and Interac e-Transfer at checkout, and free shipping over $300 CAD.
- —**Discreet, insured packaging** and Canadian support that answers.
Compare that against the default: an offshore vendor, a purity claim with no document behind it, a customs gamble and USD conversion on top.
Frequently asked questions
What is retatrutide?
Retatrutide (LY3437943), listed here as GLP-3/RT, is a synthetic triple-hormone-receptor agonist acting on the GIP, GLP-1 and glucagon receptors. It is an investigational compound in Phase 3 trials, not approved by any regulator, and is supplied for laboratory research use only.
How much weight loss did retatrutide produce in trials?
In the pivotal TRIUMPH-1 Phase 3 trial reported May 21, 2026, participants on 12 mg showed a mean 28.3% reduction in body weight at 80 weeks, an average of 70.3 lb (31.9 kg), versus 2.2% for placebo. A 104-week extension in participants with BMI 35 or above reached 30.3%, averaging 85 lb (38.6 kg).
Is retatrutide better than tirzepatide?
Across separate trials, retatrutide's peak reported weight reduction of 28.3% at 80 weeks exceeds tirzepatide's 22.5% in SURMOUNT-1 at 72 weeks. No head-to-head trial has been published, so the comparison is directional rather than definitive.
Is retatrutide FDA approved?
No. Lilly has stated it plans to submit a Biologics License Application to the FDA in Q1 2027. Retatrutide is not approved by the FDA, Health Canada or the EMA.
What are retatrutide's side effects in trials?
Predominantly gastrointestinal. At 12 mg in TRIUMPH-1: nausea 42.4%, diarrhea 32.0%, and 11.3% discontinuation due to adverse events versus 4.9% on placebo.
Can I buy retatrutide in Canada?
GLP-3/RT is available from Popular Peptides for laboratory research use, shipped domestically from Vancouver with a third-party certificate of analysis verifiable by lot number. It is not approved for therapeutic use and is not sold for human or veterinary consumption.
How much does retatrutide cost in Canada?
GLP-3/RT is supplied as a single lyophilised 10 mg vial, lot-tested, with the current per-vial price shown on the GLP-3/RT product page. It ships domestically from Vancouver, so there is no customs step and no import brokerage fee — the two charges that routinely make an offshore order cost more than its sticker price suggested. Supplied for laboratory research use only.
Sources
- —Eli Lilly and Company, TRIUMPH-1 pivotal Phase 3 topline results, May 21, 2026
- —Eli Lilly and Company, TRIUMPH-2 and TRIUMPH-3 Phase 3 results, July 23, 2026
- —Jastreboff AM et al., Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial, New England Journal of Medicine, June 26, 2023
- —Wilding JPH et al., Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1), New England Journal of Medicine, 2021
- —Jastreboff AM et al., Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1), New England Journal of Medicine, June 4, 2022
GLP-3/RT is supplied for in vitro laboratory research use only. It is not approved by Health Canada for therapeutic use and is not intended for human or veterinary consumption. 18+.
Every batch we sell is independently third-party tested, with the full Certificate of Analysis published and checkable by lot number.