The main difference in retatrutide vs tirzepatide is how many hormone signals each one copies. Tirzepatide acts on two hormone receptors, GIP and GLP-1. Retatrutide acts on those same two plus a third one, the glucagon receptor. Tirzepatide is an approved prescription drug, while retatrutide is still an experimental drug in late-stage clinical trials.
In separate trials, the top retatrutide dose led to more average weight loss than the top tirzepatide dose. But those trials used different people, lengths and designs, so the numbers cannot be lined up one to one. A direct head-to-head trial is running, and its results had not been reported as of October 2026.
Key takeaways
- Tirzepatide is a dual agonist (it switches on two receptors). Retatrutide is a triple agonist (it switches on three).
- Counting everyone who started treatment, retatrutide’s main phase 3 trial reported average weight loss of up to 25.0% at 80 weeks. Tirzepatide’s main obesity trial, measured the same way, reported up to 20.9% at 72 weeks.
- Stomach and gut side effects were the most common for both. Retatrutide trials also reported a skin sensation side effect called dysesthesia.
- Retatrutide is not approved anywhere. The maker has said it plans to file with the FDA in early 2027.
Retatrutide vs Tirzepatide at a Glance
| Feature | Tirzepatide | Retatrutide |
|---|---|---|
| Type | Dual agonist peptide | Triple agonist peptide |
| Receptors it acts on | GIP, GLP-1 | GIP, GLP-1, glucagon |
| Common nicknames | Tirz, Mounjaro, Zepbound (brand names) | Reta, “GLP-3” (informal) |
| Development stage | Approved prescription drug | Phase 3 trials, not approved |
| Main obesity trial result | Up to 20.9% average weight loss at 72 weeks (SURMOUNT-1) | Up to 25.0% average weight loss at 80 weeks (TRIUMPH-1), or 28.3% in people who stayed on treatment |
| Most common side effects | Nausea, diarrhea, vomiting, constipation | Nausea, diarrhea, constipation, vomiting, dysesthesia |
| Maker | Eli Lilly | Eli Lilly |
Both peptides are made by the same company, and both are given as a once-weekly injection in trials.
What Is Tirzepatide?
Tirzepatide is a lab-made peptide that copies two gut hormones, GIP and GLP-1. Both are incretins, which are hormones your gut releases after you eat. They help tell the body that food has arrived.
Here is what each one does in simple terms:
- GLP-1 (glucagon-like peptide-1): signals the pancreas to release insulin when blood sugar rises, slows how fast the stomach empties, and sends “I’m full” signals to the brain.
- GIP (glucose-dependent insulinotropic polypeptide): also helps release insulin after meals and appears to play a role in how the body handles fat and energy.
Because tirzepatide acts on both receptors, it is called a dual agonist. An agonist is a compound that switches on a receptor, much like a key turning a lock. Eli Lilly describes it as the first approved treatment that activates both the GIP and GLP-1 receptors (Lilly).
What Is Retatrutide?
Retatrutide (code name LY3437943) is an experimental peptide that acts on three receptors: GIP, GLP-1 and glucagon. That makes it a triple agonist. Online, people often shorten it to “reta”.
You may also see it called a “GLP-3” peptide. This is only a nickname. There is no hormone called GLP-3. The name is a shorthand for “the next step after GLP-1 drugs”, and it points to the three hormone targets.
Glucagon is the new piece. It is a hormone from the pancreas that normally raises blood sugar between meals. It also tells the liver to burn stored energy. Researchers think adding a glucagon signal may raise the energy the body uses, while the GLP-1 and GIP signals lower appetite.
Retatrutide is being tested in a set of phase 3 trials called TRIUMPH. Outside these trials, it is sold only as a research compound for lab use. Researchers often source research peptides like retatrutide from trusted platforms such as PeptidePro, and they usually check for a certificate of analysis (COA), a lab report that confirms what is in the vial and how pure it is. These compounds are supplied for research use only, not for human consumption.
How Do Retatrutide and Tirzepatide Work Differently?
Think of the body’s appetite and energy system as a car. GLP-1 and GIP mostly work the brake, so you want to eat less. Glucagon works more like the engine, nudging the body to burn more fuel. Tirzepatide presses the brake from two sides. Retatrutide presses the same brake and also revs the engine a little.
| Receptor | What it mainly does | Tirzepatide | Retatrutide |
|---|---|---|---|
| GLP-1 | Lowers appetite, slows stomach emptying, helps insulin release | Yes | Yes |
| GIP | Helps insulin release, may affect fat handling | Yes | Yes |
| Glucagon | Tells the liver to release and burn stored energy | No | Yes |
The glucagon part is the key difference in the tirzepatide vs retatrutide comparison. It is also what sets apart mazdutide, another glucagon-acting peptide that acts on GLP-1 and glucagon but not GIP. Glucagon on its own raises blood sugar, so these drugs are designed to balance it with the insulin-raising effects of GLP-1 and GIP.
Retatrutide vs Tirzepatide Weight Loss: What the Trials Show
All the studies below are human randomized controlled trials. In this type of study, people are split by chance into a drug group or a placebo group (a dummy injection), so the results can be compared fairly. Each trial compared a few fixed weekly doses, such as the retatrutide doses studied in TRIUMPH, and weight loss grew as the dose went up. The table shows the highest-dose group.
| Trial | Peptide | Study type and people | Length | Average weight loss, top dose | Placebo |
|---|---|---|---|---|---|
| SURMOUNT-1 (2022) | Tirzepatide | Phase 3, 2,539 adults with obesity, no diabetes | 72 weeks | 20.9% | 3.1% |
| Phase 2 trial (2023) | Retatrutide | Phase 2, 338 adults with obesity, no diabetes | 48 weeks | 24.2% | 2.1% |
| TRIUMPH-1 (2026) | Retatrutide | Phase 3, 2,339 adults with obesity, no diabetes | 80 weeks | 25.0% (28.3% in those who stayed on it) | 3.9% (2.2%) |
| TRIUMPH-2 (2026) | Retatrutide | Phase 3, 1,152 adults with obesity and type 2 diabetes | 80 weeks | 20.8% | Not stated in release |
| TRIUMPH-3 (2026) | Retatrutide | Phase 3, 1,949 adults with severe obesity and heart disease | 80 weeks | 22.6% | Not stated in release |
Why the numbers cannot be compared directly
These trials enrolled different people, ran for different lengths of time and were done years apart. Longer trials usually show more weight loss, because people keep losing weight for many months. So a 28% result at 80 weeks and a 21% result at 72 weeks do not prove one drug is stronger.
The TRIUMPH-1 figures were reported by Eli Lilly in a company release. Company releases give early results that have not yet gone through full peer review in a journal.
Is there a head-to-head trial?
Yes. TRIUMPH-5 is a phase 3 trial that compares retatrutide directly with tirzepatide in adults with obesity, with percent weight change as the main result (EU trial register). It started in October 2024 and runs for 80 weeks of treatment. Its results had not been released as of October 2026.
Does Retatrutide Burn Fat or Muscle?
The short answer: studies so far suggest most of the weight lost is fat, but some lean mass is lost too. This is true for almost any large weight loss, whether from diet, surgery or medicine.
Lean mass is everything in the body that is not fat. It includes muscle, but also water, organs and bone. So a drop in lean mass is not the same as a drop in muscle alone. Researchers measure it with a DXA scan, a low-dose X-ray that separates fat from lean tissue.
| Study | Study type | What it found |
|---|---|---|
| SURMOUNT-1 body composition substudy (tirzepatide) | Human trial substudy, 160 people, 72 weeks | Fat mass fell 33.9% and lean mass fell 10.9%. About 75% of the weight lost was fat and 25% was lean mass. |
| Retatrutide body composition substudy (Lancet Diabetes & Endocrinology, 2025) | Phase 2 human trial substudy, 189 adults with type 2 diabetes, 36 weeks | Fat mass fell by up to 26.1%. The authors reported that lean mass was not lost out of proportion to total weight loss. |
The big TRIUMPH-1 trial release did not include body composition results. So for retatrutide vs tirzepatide muscle loss, there is no direct comparison yet. Researchers expect more data from the phase 3 program.
Is Retatrutide Better Than Tirzepatide?
On weight loss numbers alone, retatrutide looks stronger in its trials. But “better” depends on more than one number, and the evidence is not equal yet.
| Question | Tirzepatide | Retatrutide |
|---|---|---|
| Largest average weight loss reported | About 21% at 72 weeks | About 25% to 28% at 80 weeks |
| Head-to-head result | Not yet available | Not yet available |
| Years of real-world use | Several years as an approved drug | None outside trials |
| Published long-term safety data | Larger and longer | Still building |
| Stopped treatment due to side effects (top dose) | 6.2% in SURMOUNT-1 | 11.3% in TRIUMPH-1 |
So when people ask what is more powerful than tirzepatide, retatrutide is the main name that comes up. Researchers will not know if it is truly better, and for whom, until TRIUMPH-5 reports and the full phase 3 data are published.
How Do They Compare With Semaglutide (Ozempic)?
Semaglutide, sold as Ozempic and Wegovy, acts on only one receptor: GLP-1. So the three peptides form a simple ladder:
- Semaglutide: one receptor (GLP-1)
- Tirzepatide: two receptors (GLP-1 and GIP)
- Retatrutide: three receptors (GLP-1, GIP and glucagon)
Tirzepatide and semaglutide have been compared directly. In the SURMOUNT-5 trial of 751 adults with obesity, tirzepatide led to 20.2% average weight loss at 72 weeks, compared with 13.7% for semaglutide (Aronne et al., NEJM 2025). That gap is a big part of why the tirzepatide vs semaglutide question gets so much attention. For semaglutide vs tirzepatide vs retatrutide, no single trial has tested all three side by side.
Retatrutide vs Tirzepatide Side Effects Reported in Trials
For both peptides, the most common side effects in trials were stomach and gut problems. These were mostly mild to moderate and showed up most often while the dose was being raised.
| Side effect | Tirzepatide (SURMOUNT-1) | Retatrutide (TRIUMPH-1) |
|---|---|---|
| Most common | Nausea, diarrhea, vomiting, constipation | Nausea, diarrhea, constipation, vomiting |
| Nausea | Common, mostly during dose increases | 28.6% to 42.4% vs 14.8% on placebo |
| Dysesthesia | Not among its common side effects | 5.1% to 12.5% vs 0.9% on placebo |
| Stopped due to side effects | 4.3% to 7.1% vs 2.6% on placebo | 4.1% to 11.3% vs 4.9% on placebo |
Dysesthesia means unusual skin sensations, such as tingling, burning or skin that feels sensitive to touch. Lilly reported that most cases were mild to moderate. In the TRIUMPH-4 trial, it was reported in 20.9% of people on the top dose (Patient Care). The cause is not yet clear.
Tirzepatide’s label carries a boxed warning, the FDA’s strongest warning, about thyroid C-cell tumors, based on findings in rodents (Lilly). Since retatrutide is still in trials, its full safety profile is not known. Fast weight loss from any cause also brings its own concerns, which come up often in discussions on peptides and weight loss safety.
Approval and Sport Status
| Tirzepatide | Retatrutide | |
|---|---|---|
| Approval status | Approved prescription drug (Mounjaro, Zepbound) | Not approved; Lilly plans to file with the FDA in early 2027 (Lilly) |
| WADA status | Not prohibited; on the 2026 Monitoring Program | Not named on the list; may fall under the rule for non-approved substances |
In sport, the World Anti-Doping Agency (WADA) does not ban GLP-1 drugs. It added tirzepatide to its 2026 Monitoring Program, which tracks how often a substance shows up in athletes’ samples without banning it (EMJ). Retatrutide is different because it is not approved anywhere. WADA’s S0 category covers drugs that are not approved for human use, so athletes should check with their anti-doping body.
Frequently Asked Questions
Is retatrutide better than tirzepatide?
In separate trials, retatrutide led to more average weight loss than tirzepatide, about 25% at 80 weeks vs about 21% at 72 weeks when counting everyone who started. But the trials differ, retatrutide is not approved, and its long-term safety is less known. The head-to-head TRIUMPH-5 trial should give a clearer answer.
Does retatrutide burn fat or muscle?
Early research suggests most of the weight lost with retatrutide is fat. A phase 2 substudy in adults with type 2 diabetes found fat mass fell by up to 26.1% over 36 weeks, without an outsized loss of lean mass. Some lean mass is lost with almost any large weight loss, so more data are needed.
Does retatrutide work immediately?
No. In trials, weight loss built up slowly over months. In the phase 2 trial, the top-dose group had lost 17.5% of body weight at 24 weeks and 24.2% at 48 weeks. Doses were raised step by step at the start, partly to limit stomach side effects.
Can retatrutide and tirzepatide be taken together?
No published trial has studied retatrutide and tirzepatide together. Both act on the same GLP-1 and GIP receptors, so combining them would double up on the same signals, and the effects are unknown. In trials, they are studied as separate options, and TRIUMPH-5 compares one against the other.
Why is retatrutide called GLP-3?
“GLP-3” is an informal nickname, not a scientific name. There is no hormone called GLP-3. People use it because retatrutide acts on three hormone receptors (GLP-1, GIP and glucagon), and they see it as the next step after GLP-1 drugs like semaglutide and dual drugs like tirzepatide.
Disclaimer
This article is provided for educational and informational purposes only and does not constitute medical advice. The compounds discussed are research compounds and are not intended for human consumption. Anyone considering the use of any peptide should first consult a qualified, licensed healthcare professional, who can assess their individual circumstances and advise on what is most appropriate for them.
Sources cited
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). NEJM 2022. ACC summary
- Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity, a phase 2 trial. NEJM 2023. Patient Care summary
- Eli Lilly. TRIUMPH-1 results, May 21, 2026. Lilly release
- Eli Lilly. TRIUMPH-2 and TRIUMPH-3 results, July 23, 2026. Lilly release
- TRIUMPH-4 results, December 11, 2025. Patient Care
- TRIUMPH-5 trial record. EU Clinical Trials Register
- Look M, et al. Body composition changes with tirzepatide in SURMOUNT-1. Diabetes Obes Metab 2025. Abstract
- Retatrutide body composition substudy. Lancet Diabetes Endocrinol 2025. MIMS summary
- Aronne LJ, et al. Tirzepatide as compared with semaglutide (SURMOUNT-5). NEJM 2025. ACC summary
- Eli Lilly. FDA approves Zepbound, November 8, 2023. Lilly release
- GLP-1 drugs on the WADA 2026 Monitoring Program. EMJ