- In the phase 3 TRIUMPH-1 trial, adults with obesity and without diabetes on the highest dose of retatrutide (12 mg weekly) lost 25.0% of their body weight on average over 80 weeks, vs 3.9% on placebo.2
- In TRIUMPH-2, adults with type 2 diabetes lost 18.8% on 12 mg, vs 5.1% on placebo.3
- Retatrutide is not approved by the FDA. Products sold online as "research peptides" are not the medicine tested in these trials.6
What is retatrutide?
Retatrutide is an experimental once-weekly injection made by Eli Lilly. Semaglutide (Wegovy, Ozempic) acts on one hormone receptor, GLP-1. Tirzepatide (Zepbound, Mounjaro) acts on two, GLP-1 and GIP. Retatrutide adds a third, the glucagon receptor, which is why it is often called a "triple agonist".1
Researchers are testing it for obesity, type 2 diabetes, knee osteoarthritis and sleep apnea. Every trial described here was funded by Lilly.
Is retatrutide FDA approved?
No. A trial paper published in October 2026 still describes retatrutide as investigational.4 The FDA has not approved it for any use. That matters, because products labeled "retatrutide" are widely sold online as "research chemicals" or "research peptides". In a December 2024 warning letter to one seller, the FDA called its retatrutide product an unapproved new drug and said that a "research chemicals only" label did not change that, because the seller's website showed the product was meant for people.6
The phase 2 trial (2023)
The first large test enrolled 338 adults with obesity, or overweight with a weight-related condition, and without diabetes. They were randomly assigned to weekly retatrutide at 1, 4, 8 or 12 mg, or placebo, for 48 weeks.1
On 12 mg, 83% of participants lost 15% or more of their weight by week 48, vs 2% on placebo.1 The trial was small and short, so phase 3 was needed to confirm it.
What did TRIUMPH-1 find?
TRIUMPH-1 is the main phase 3 trial. It enrolled 2,339 adults with obesity and without diabetes, who received weekly retatrutide at 4, 9 or 12 mg, or placebo, for 80 weeks. It was published in the New England Journal of Medicine.2
These averages count everyone assigned to a group, including people who stopped treatment. TRIUMPH-1 also included smaller groups with other conditions:2
- Knee osteoarthritis (574 people). Knee pain scores (on a 1 to 10 scale) fell by 3.5 and 3.6 points on 9 and 12 mg, vs 1.9 on placebo. Read more in GLP-1s and knee osteoarthritis.
- Obstructive sleep apnea (243 people). Breathing interruptions during sleep fell by 34.3 and 31.7 events per hour on 9 and 12 mg, vs 9.9 on placebo. A separate paper reports these results in more detail.4
What about people with type 2 diabetes?
TRIUMPH-2, published in The Lancet, enrolled 1,152 adults with type 2 diabetes and a BMI of 27 or higher, for 80 weeks.3
| Group | Average weight change at week 80 |
|---|---|
| Retatrutide 12 mg | −18.8% |
| Retatrutide 9 mg | −16.8% |
| Retatrutide 4 mg | −11.9% |
| Placebo | −5.1% |
As with other medicines in this class, people with diabetes lost less weight than people without it. Blood sugar control also improved.3 See GLP-1 weight loss with type 2 diabetes for why.
What are the side effects of retatrutide?
Stomach and gut side effects were the most common in every trial. In phase 2, they rose with the dose, were mostly mild to moderate, and were partly reduced by starting at a lower dose. Heart rate went up with the dose, peaked at 24 weeks, and then declined.1
TRIUMPH-2 reports the clearest numbers so far:3
| Side effect | Placebo | 4 mg | 9 mg | 12 mg |
|---|---|---|---|---|
| Diarrhea | 13% | 27% | 34% | 34% |
| Nausea | 8% | 14% | 21% | 28% |
| Dysesthesia (unusual skin sensation) | 1% | 4% | 6% | 7% |
| Low blood pressure | <1% | 1% | 5% | 6% |
| Stopped due to side effects or death | 5% | 4% | 12% | 8% |
For tips that help with stomach side effects of this drug class, see GLP-1 nausea and stomach side effects. Longer-term safety data will come from trials still under way.
Retatrutide vs tirzepatide
No trial comparing retatrutide with tirzepatide has been published. The closest context is SURMOUNT-1, a separate trial in adults with obesity and without diabetes, where weekly tirzepatide 15 mg led to 20.9% average weight loss at 72 weeks, vs 3.1% on placebo.5
| Trial | Medicine | Length | Medicine | Placebo |
|---|---|---|---|---|
| SURMOUNT-1 | Tirzepatide 15 mg | 72 weeks | −20.9% | −3.1% |
| TRIUMPH-1 | Retatrutide 12 mg | 80 weeks | −25.0% | −3.9% |
What about retatrutide dosage?
The trials tested weekly doses of 1 to 12 mg, raised in steps. Those doses describe what was studied, not what anyone should take. There is no approved dose, because there is no approved product. Any future dosing will be set by regulators and prescribers.
Common questions
How much weight do people lose on retatrutide?
In the phase 3 TRIUMPH-1 trial of 2,339 adults with obesity and without diabetes, people on the 12 mg weekly dose lost 25.0% of their body weight on average over 80 weeks, compared with 3.9% on placebo. In TRIUMPH-2, in adults with type 2 diabetes, the 12 mg dose led to an average loss of 18.8% vs 5.1% on placebo.
Is retatrutide FDA approved?
No. As of November 2026, retatrutide is an investigational medicine and is not approved by the FDA for any use. The FDA has issued warning letters to online sellers of products labeled retatrutide, calling them unapproved new drugs.
What are the side effects of retatrutide?
Stomach and gut side effects were the most common in trials. In TRIUMPH-2, in adults with type 2 diabetes, diarrhea was reported by 27% to 34% of people on retatrutide vs 13% on placebo, and nausea by 14% to 28% vs 8%. Dysesthesia, an unusual skin sensation, was reported by 4% to 7% vs 1% on placebo.
Is retatrutide stronger than tirzepatide?
No trial comparing them head to head has been published. In separate trials, retatrutide 12 mg led to 25.0% average weight loss at 80 weeks in TRIUMPH-1, and tirzepatide 15 mg led to 20.9% at 72 weeks in SURMOUNT-1, but the trials differed in length and participants.
Sources
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. PubMed · doi:10.1056/NEJMoa2301972
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity (TRIUMPH-1). N Engl J Med. 2026;395(18):1781-1793. PubMed · doi:10.1056/NEJMoa2604169
- Bellido V, le Roux CW, Ekinci EI, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial. Lancet. 2026;408(10563):1455-1472. PubMed · doi:10.1016/S0140-6736(26)01861-1
- Grunstein RR, Somers VK, Azarbarzin A, et al. Retatrutide Once Weekly for Treatment of Obstructive Sleep Apnea. N Engl J Med. 2026 (online ahead of print). PubMed · doi:10.1056/NEJMoa2611477
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PubMed · doi:10.1056/NEJMoa2206038
- U.S. Food and Drug Administration. Warning letter to Swisschems (MARCS-CMS 695663). December 10, 2024. FDA
