Quick Answer: Retatrutide is an investigational weekly injection from Eli Lilly that targets three hormone receptors (GLP-1, GIP and glucagon), one more than Zepbound and two more than Wegovy. In the main Phase 3 obesity trial, TRIUMPH-1, people on the highest dose lost an average of 28.3% of their body weight (about 70 pounds) over 80 weeks. It is not FDA approved. Lilly says it plans to apply for approval in the first quarter of 2027, so it can't be legally prescribed or bought yet. Products sold online as "retatrutide" are unapproved and unregulated.
Educational information only. This is not medical advice.
What Is Retatrutide?
Retatrutide is a once-weekly injection in development for obesity and related conditions. It's called a "triple agonist" because it activates three hormone receptors that the current medications only partly cover:1
- GLP-1 slows digestion, reduces appetite and helps you feel full. This is what semaglutide (Ozempic, Wegovy) targets.
- GIP works with GLP-1 on appetite and blood sugar. Tirzepatide (Mounjaro, Zepbound) targets both GLP-1 and GIP.
- Glucagon is the new addition. Glucagon signals the liver to release stored energy and may raise energy expenditure, which researchers think helps explain the larger weight loss.1
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What the Phase 3 Trials Show
Lilly has now reported results from several Phase 3 TRIUMPH trials:
| Trial | Who was studied | Average weight loss, highest dose |
|---|---|---|
| TRIUMPH-4 (reported Dec 2025) | Obesity or overweight with knee osteoarthritis | 28.7% at 68 weeks2 |
| TRIUMPH-1 (reported May 2026) | 2,339 adults with obesity or overweight, without diabetes | 28.3% at 80 weeks (vs. 2.2% on placebo); 30.3% at 104 weeks in an extension3 |
| TRIUMPH-2 (reported July 2026) | Adults with type 2 diabetes and obesity or overweight | 20.8% at 80 weeks, with A1C down about 1.5 points4 |
| TRIUMPH-3 (reported July 2026) | Severe obesity with established heart disease | Up to 22.6% at 80 weeks5 |
In TRIUMPH-1, the 4 mg, 9 mg and 12 mg doses produced average losses of 19.0%, 25.9% and 28.3% for people who stayed on treatment, or 17.6%, 23.7% and 25.0% counting everyone who started.3 As with other GLP-1 medications, people with type 2 diabetes lost less weight.
How it compares with current medications
In their own trials, semaglutide 2.4 mg (Wegovy) produced roughly 15% average weight loss and tirzepatide (Zepbound) roughly 20%. Retatrutide's numbers are higher, but no head-to-head trial has compared them, and trial populations and lengths differ, so direct comparisons are approximate.
Side Effects
The side effects in TRIUMPH-1 were similar in type to other GLP-1 medications, but more frequent at higher doses. At the 12 mg dose versus placebo:3
- Nausea: 42.4% vs. 14.8%
- Diarrhea: 32.0% vs. 13.5%
- Constipation: 26.1% vs. 10.9%
- Vomiting: 25.3% vs. 4.8%
- Dysesthesia (abnormal skin sensations such as tingling or sensitivity): 12.5% vs. 0.9%. Lilly reported these were generally mild to moderate and most resolved during treatment.
About 11% of people on the 12 mg dose stopped treatment because of side effects, compared with about 5% on placebo.3 Long-term safety data are still being collected.
When Will Retatrutide Be Available?
Retatrutide is not FDA approved. After TRIUMPH-2 results, Lilly said it plans to submit its application to the FDA in the first quarter of 2027.4 FDA reviews commonly take about 10-12 months, so approval would most likely come in late 2027 or later, if it is approved.
Warning about online "retatrutide": Retatrutide can only be legally obtained through a clinical trial. Products sold online, at clinics or in stores as retatrutide or as a "research peptide" are unapproved and unregulated, may not contain what the label says, and have been linked to hospitalizations.6 Lilly has sued several sellers over illegal sales. If you want to try a GLP-1 medication now, talk to a prescriber about the approved options.
What It Means for How You Eat
Retatrutide isn't available, but the nutrition lessons from current GLP-1 medications apply even more to a drug that produces larger weight loss. The bigger the weight loss, the more it matters that most of it comes from fat rather than muscle.
- Protein first: about 1.2-1.6 g per kg of body weight a day, or roughly 80-120 grams for most people, spread across 3-4 meals.7
- Strength training: at least 2-3 sessions a week to protect muscle.7
- Small, gentle meals: lean protein, vegetables and modest portions of easy carbs, with greasy and fried foods kept to a minimum during dose increases.
- Fluids: spread through the day, especially when GI side effects flare.
Our guides to preventing muscle loss on GLP-1 medications and the GLP-1 diet cover this in detail. If you're starting a GLP-1 now, our GLP-1 Meal Plan delivers high-protein, portion-controlled meals that are ready in minutes, with no subscription required.
Frequently Asked Questions
Is retatrutide FDA approved?
No. Retatrutide is still investigational. Lilly says it plans to submit an application to the FDA in the first quarter of 2027. Until it is approved, it can't be legally prescribed or sold outside clinical trials.
How much weight can you lose on retatrutide?
In the TRIUMPH-1 trial of adults with obesity or overweight and without diabetes, people on the 12 mg dose lost an average of 28.3% of their body weight (about 70 pounds) over 80 weeks, versus 2.2% on placebo. People with type 2 diabetes lost about 21% on the same dose in TRIUMPH-2.
How is retatrutide different from Ozempic or Mounjaro?
Retatrutide activates three hormone receptors (GLP-1, GIP and glucagon). Ozempic activates one (GLP-1) and Mounjaro two (GLP-1 and GIP). The added glucagon activity may increase energy use, which may help explain the larger weight loss seen in trials.
What are the side effects of retatrutide?
Mostly gastrointestinal: in TRIUMPH-1, nausea affected about 42% of people on the 12 mg dose, diarrhea 32%, constipation 26% and vomiting 25%. About 12.5% reported dysesthesia, an abnormal skin sensation, which was generally mild to moderate. About 11% on the top dose stopped because of side effects.
Is it safe to buy retatrutide online?
No. Retatrutide isn't approved, so anything sold online or as a "research peptide" is unregulated and may not contain what it claims. These products have been linked to hospitalizations, and Lilly has sued sellers over illegal sales.
What should you eat while taking a GLP-1 medication like retatrutide?
Prioritize protein (roughly 80-120 grams a day spread across meals), eat smaller and gentler meals, include fiber-rich vegetables, drink fluids through the day, and strength train at least 2-3 times a week to protect muscle.
References
- 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.
- Eli Lilly and Company. Retatrutide TRIUMPH-4 topline results. Press release. December 11, 2025.
- Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. May 21, 2026. Link
- Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction (TRIUMPH-2). September 29, 2026. Link
- Phase III trials confirm benefits of Lilly's triple agonist retatrutide. Drug Discovery World. July 28, 2026. Link
- Public Citizen. Hospitalizations, enforcement gaps, influencers tied to unapproved retatrutide products. 2026. Link
- Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory. Am J Clin Nutr. 2025. Full text
This content is for educational purposes only and is not a substitute for advice from a qualified healthcare professional.
