Important: Retatrutide is an investigational medication currently in Phase 3 clinical trials. It has not been approved by the U.S. Food and Drug Administration (FDA) and is not available for prescription. The information in this article is for educational purposes only, based on published clinical trial data, and does not constitute medical advice or promotion of an unapproved therapy.
Weight Loss & Metabolic Health
RETATRUTIDE: THE TRIPLE AGONIST
The first drug to activate all three metabolic receptors at once. What the science says, what the trials show, and what it means for the future of weight loss.
Medically reviewed by Missy Zammichieli, DNP, APRN, FNP-BC · Updated March 25, 2026
Explore Current GLP-1 Options
WHAT IS RETATRUTIDE?
Retatrutide (LY3437943) is an investigational medication developed by Eli Lilly. It is a single synthetic peptide that simultaneously activates three different metabolic receptors: GLP-1, GIP, and glucagon. This makes it the first triple-agonist in the incretin drug class.
To understand why this matters, you need to understand what each receptor does when activated.
GLP-1 Receptor
The Appetite Brake
GLP-1 (glucagon-like peptide-1) slows gastric emptying, signals satiety to the brain, and stimulates insulin release. This is the receptor targeted by semaglutide (Ozempic/Wegovy). It is the most validated pathway for weight loss.
GIP Receptor
The Metabolic Optimizer
GIP (glucose-dependent insulinotropic polypeptide) enhances insulin sensitivity, improves lipid metabolism, and may influence how the body stores and utilizes fat. Tirzepatide (Mounjaro/Zepbound) activates both GLP-1 and GIP. Adding GIP to GLP-1 appears to amplify weight loss beyond what GLP-1 alone achieves.
Glucagon Receptor
The Metabolic Accelerator
Glucagon increases energy expenditure, stimulates hepatic fat oxidation (your liver burns its own fat stores), and may help preserve lean body mass during weight loss. This is what retatrutide adds to the equation. No approved weight loss drug targets this receptor.
The analogy: Think of weight loss drugs as levers you can pull. Semaglutide pulls one lever (GLP-1) — it reduces appetite. Tirzepatide pulls two levers (GLP-1 + GIP) — it reduces appetite and optimizes metabolism. Retatrutide pulls three levers (GLP-1 + GIP + glucagon) — it reduces appetite, optimizes metabolism, and actively increases the rate at which your body burns stored energy. Each generation adds a new mechanism of action.
Reference: Coskun T, et al. "LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist for glycemic control and weight loss." Cell Metab. 2022;34(9):1234-1247.
HOW RETATRUTIDE DIFFERS FROM EXISTING DRUGS
The GLP-1 drug class has evolved in three distinct generations. Each added a new receptor target and produced incrementally more weight loss.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Brand Names | Ozempic, Wegovy | Mounjaro, Zepbound | None (investigational) |
| Manufacturer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Mechanism | GLP-1 agonist | GLP-1 + GIP dual agonist | GLP-1 + GIP + glucagon triple agonist |
| Avg Weight Loss | ~15-17% (STEP trials) | ~20-22% (SURMOUNT trials) | ~24% (Phase 2, 12 mg) |
| Injection Frequency | Once weekly | Once weekly | Once weekly |
| FDA Status | Approved (2017/2021) | Approved (2022/2023) | Phase 3 trials |
| Key Trial | STEP program | SURMOUNT program | TRIUMPH program |
Important caveat: Cross-trial comparisons are unreliable. The STEP, SURMOUNT, and retatrutide Phase 2 trials used different patient populations, different baseline characteristics, and different protocols. The only way to know if retatrutide truly produces more weight loss than existing drugs is a head-to-head randomized trial. None exists yet.
PHASE 2 RESULTS
The Phase 2 dose-ranging trial, published in the New England Journal of Medicine in June 2023, is the primary source of clinical data on retatrutide for obesity. Here are the key numbers.
Study Design
338 adults with obesity (BMI 30+) or overweight (BMI 27+) with at least one weight-related comorbidity. Randomized to placebo or one of four retatrutide dose levels (1 mg, 4 mg, 8 mg, 12 mg). Duration: 48 weeks.
Primary Outcome
Percent change in body weight from baseline at 24 weeks. Weight loss continued through 48 weeks, and the curve had not fully plateaued at study end — suggesting even greater loss with longer treatment.
Weight Loss by Dose (48 Weeks)
-8.7%
1 mg
-17.1%
4 mg
-22.8%
8 mg
-24.2%
12 mg
Placebo group: -2.1%. All dose groups significantly different from placebo (p<0.001).
What this means: At the highest dose, participants lost nearly a quarter of their body weight in under a year. For context, that means a 250-pound person losing approximately 60 pounds. At 12 mg, 100% of participants lost at least 5% of their body weight, and more than 90% lost at least 10%. These are preliminary Phase 2 numbers. Phase 3 will determine whether this holds up in a larger, more diverse population.
For a detailed breakdown of the trial data, methodology, and subgroup analyses: Retatrutide Clinical Trials Deep Dive →
Reference: Jastreboff AM, et al. "Triple-Hormone-Receptor Agonist Retatrutide for Obesity." N Engl J Med. 2023;389(6):514-526.
PHASE 3: THE TRIUMPH PROGRAM
Eli Lilly launched the TRIUMPH Phase 3 clinical trial program to evaluate retatrutide at scale. These trials will determine whether retatrutide receives FDA approval for obesity and type 2 diabetes.
Phase 3 trials are larger (thousands of participants vs. hundreds), longer, more diverse in patient population, and designed to detect less common side effects. Phase 2 data is promising, but Phase 3 is what actually matters for approval.
TRIUMPH-1
Obesity without type 2 diabetes. This is the pivotal weight loss trial — the one most comparable to STEP 1 (semaglutide) and SURMOUNT-1 (tirzepatide).
TRIUMPH-2
Type 2 diabetes with obesity. Evaluates glycemic control alongside weight loss. Head-to-head comparison with tirzepatide would be ideal but is not confirmed.
TRIUMPH-3
Obesity with cardiovascular risk factors. Evaluates cardiovascular outcomes — a critical regulatory endpoint now expected for obesity drugs.
TRIUMPH-4
Weight maintenance after initial loss. Examines whether retatrutide can maintain weight loss long-term — the key weakness of all current weight loss interventions.
What we're watching for: Whether the ~24% weight loss from Phase 2 holds up. Whether the glucagon component creates any unexpected safety signals at scale. Whether there's a cardiovascular benefit. And critically, whether the weight stays off.
Detailed trial-by-trial analysis: Retatrutide Clinical Trials Deep Dive →
THE GLUCAGON ADVANTAGE
The glucagon receptor is what makes retatrutide fundamentally different — not just a stronger version of existing drugs, but a mechanistically distinct approach. Every other GLP-1 medication works primarily by reducing energy intake (you eat less). Glucagon receptor activation adds a second variable: increasing energy expenditure (you burn more).
This is the most important conceptual shift in the drug's design. Instead of relying solely on appetite suppression, retatrutide attacks obesity from both sides of the energy balance equation.
Increased Energy Expenditure
Glucagon receptor activation increases resting metabolic rate — your body burns more calories even at rest. This is unique among GLP-1 class drugs. In preclinical models, the glucagon component increased energy expenditure by 15-20% above baseline.
Hepatic Fat Oxidation
Glucagon signals the liver to mobilize and burn its own fat stores. This is particularly relevant for patients with metabolic-associated steatotic liver disease (MASLD, formerly NAFLD). A separate Phase 2 trial showed retatrutide reduced liver fat by up to 86% — a staggering number.
Potential Lean Mass Preservation
Early data suggests the glucagon component may help preserve lean body mass during weight loss. The mechanism: by increasing energy expenditure and fat oxidation, the body preferentially burns fat rather than breaking down muscle for energy. This needs confirmation in Phase 3 body composition sub-studies.
Why this matters clinically: The two biggest problems with current GLP-1 weight loss medications are (1) muscle loss during treatment and (2) metabolic adaptation that makes weight regain likely after stopping. If glucagon receptor agonism addresses both — by preserving muscle and increasing metabolic rate — retatrutide could represent a genuine step-change, not just an incremental improvement.
Reference: Sanyal AJ, et al. "A Phase 2 Randomized Trial of Survodutide in MASH and Fibrosis." Nat Med. 2024. (Note: Survodutide is a glucagon/GLP-1 dual agonist; retatrutide's MASLD data from Loomba et al., presented at AASLD 2023.)
SIDE EFFECTS
The side effect profile from the Phase 2 trial follows the same pattern as other GLP-1 medications: primarily gastrointestinal, primarily during dose escalation, and primarily mild to moderate.
Nausea: The most commonly reported side effect. At the 12 mg dose, approximately 45% of participants experienced nausea, compared to ~10% on placebo. Most episodes were mild to moderate and concentrated in the first 4-8 weeks during dose escalation.
Diarrhea: Reported in approximately 30% of participants at 12 mg. Generally mild and transient.
Vomiting: Less common than nausea, reported in approximately 15-20% at higher doses. Most episodes occurred during the first few weeks.
Constipation: Reported in approximately 10-15% of participants. Consistent with the GLP-1 class effect of slowed gastric motility.
Decreased appetite: Common, but also the intended therapeutic effect. Some participants reported appetite suppression strong enough to require attention to maintaining adequate protein and caloric intake.
The glucagon question: Because glucagon raises blood glucose, there was concern about hyperglycemia. In the Phase 2 trial, the GLP-1 and GIP components effectively counterbalanced this effect — blood sugar levels actually improved. No clinically significant hyperglycemia was observed. This will be closely monitored in Phase 3.
Full side effect analysis with dose-by-dose breakdown: Retatrutide Side Effects Deep Dive →
FDA TIMELINE
As of March 2026, here is the current regulatory status.
Completed: Phase 2 (Obesity)
Results published in NEJM, June 2023. Demonstrated 24.2% weight loss at highest dose over 48 weeks.
Completed: Phase 2 (Type 2 Diabetes)
Results published in The Lancet, 2023. Demonstrated significant HbA1c reduction alongside weight loss.
In Progress: Phase 3 (TRIUMPH Program)
Multiple trials actively enrolling and running. TRIUMPH-1 (obesity), TRIUMPH-2 (diabetes), TRIUMPH-3 (cardiovascular), TRIUMPH-4 (weight maintenance).
Pending: FDA Submission
Eli Lilly has not announced a specific submission date. Based on typical Phase 3 durations and FDA review timelines, the earliest plausible approval would be late 2026 or 2027. This assumes positive Phase 3 results and no major safety signals.
Reality check: Drug development timelines frequently shift. Phase 3 trials can take longer than expected, the FDA can request additional data, and safety signals can emerge that require additional study. Many promising Phase 2 drugs have failed in Phase 3. Retatrutide's Phase 2 data is strong, but approval is not guaranteed and the timeline is not certain.
SHOULD I WAIT OR START NOW?
This is the most common question we get about retatrutide, and the answer is straightforward: if you meet the criteria for GLP-1 treatment today, do not wait for an unapproved drug.
Obesity is a progressive condition. Every month you delay treatment, metabolic health continues to deteriorate — insulin resistance worsens, inflammatory markers rise, cardiovascular risk accumulates, and liver fat increases. The health damage is happening now, not in some theoretical future.
Semaglutide and tirzepatide are available now, well-studied, and produce significant weight loss. Starting treatment today with an approved medication and transitioning to retatrutide later (if it proves superior after approval) is a far better strategy than waiting 1-2+ years for a drug that may or may not be approved.
The math: If you need to lose 60 pounds and you wait 18 months for retatrutide, that's 18 months of carrying excess weight with all its metabolic consequences. If you start semaglutide or tirzepatide today, you could lose 30-50 pounds in that same timeframe. Even if retatrutide eventually proves slightly more effective, the cost of delay is real and measurable.
Full analysis of the wait-vs-start decision: Should I Wait for Retatrutide? →
WHAT MOONSHOT MEDICAL OFFERS TODAY
We do not offer retatrutide — it is not FDA-approved and cannot be legally prescribed. Here is what we do offer for medical weight loss right now.
GLP-1 Medications
Semaglutide and tirzepatide prescribed by board-certified providers. Dose titration managed on an individual basis. Both brand-name and compounded options available depending on your situation and insurance.
DEXA Body Composition
Baseline and ongoing DEXA scans to track exactly what you're losing — fat vs. lean mass. This is how we catch excessive muscle loss early and adjust your protocol.
Comprehensive Blood Work
Metabolic panels, hormone levels, inflammatory markers, liver function, and more. We track biomarkers over time so we can see what's actually changing inside — not just on the scale.
Nutrition & Exercise Guidance
Protein targets, training recommendations, and lifestyle protocols designed to preserve muscle and maximize the ratio of fat-to-lean mass lost. The medication is one part of a complete program.
On retatrutide: We will evaluate retatrutide for our program if and when it receives FDA approval. If the Phase 3 data confirms the Phase 2 results, and if the safety profile is acceptable, it could become part of our weight loss toolkit. Until then, we offer the best evidence-based options currently available.
COMMON QUESTIONS
What is retatrutide?
Retatrutide (LY3437943) is an investigational triple-agonist peptide developed by Eli Lilly. It activates three metabolic receptors simultaneously — GLP-1, GIP, and glucagon — making it the first drug in its class. It is designed for the treatment of obesity and type 2 diabetes and is currently in Phase 3 clinical trials. It has not been approved by the FDA.
When will retatrutide be FDA approved?
There is no confirmed approval date. As of March 2026, retatrutide is in Phase 3 clinical trials (the TRIUMPH program). Based on typical development timelines, the earliest possible approval would be late 2026 or 2027, assuming positive results and no safety concerns. Eli Lilly has not publicly committed to a submission date. Approval is not guaranteed.
How much weight can you lose on retatrutide?
In the Phase 2 trial published in the NEJM, participants on the 12 mg dose lost an average of 24.2% of their body weight over 48 weeks. That's approximately 58 pounds for a 240-pound person. This is the highest average weight loss seen in any GLP-1 class trial. However, these are Phase 2 results with 338 participants — Phase 3 results (with thousands of participants) are needed to confirm these numbers.
Is retatrutide better than Ozempic or Mounjaro?
We don't know yet. Phase 2 data shows higher average weight loss for retatrutide than was seen in Phase 3 trials of semaglutide (Ozempic) or tirzepatide (Mounjaro), but cross-trial comparisons are unreliable. Different studies used different populations, protocols, and endpoints. No head-to-head trial exists. Until one does, the honest answer is: the Phase 2 numbers are promising but not conclusive.
What are retatrutide side effects?
The most common side effects in Phase 2 were gastrointestinal: nausea (~45% at highest dose), diarrhea (~30%), vomiting (~15-20%), and constipation (~10-15%). These were predominantly mild to moderate and occurred mainly during the initial dose escalation period. The full side effect profile will become clearer from Phase 3 data with larger patient numbers and longer follow-up.
Can I get retatrutide now?
No. Retatrutide is not approved by the FDA and cannot be legally prescribed or dispensed. The only way to access it is through enrollment in an active clinical trial. Any website, clinic, or source claiming to sell or prescribe retatrutide is either selling an unapproved product of unknown composition or operating outside FDA regulations. Do not buy it.
Can retatrutide be compounded?
No. Compounding pharmacies (both 503A and 503B facilities) can only compound drugs that have an FDA-approved reference product or that appear on specific FDA compounding lists. Since retatrutide has never been FDA-approved in any form, it cannot be legally compounded. This is different from semaglutide and tirzepatide, which can be compounded because they have approved reference products.
Does Moonshot Medical offer retatrutide?
No. We do not and cannot offer retatrutide because it is not FDA-approved. We currently offer semaglutide and tirzepatide as part of our comprehensive weight loss program, which includes DEXA body composition tracking, blood work, nutrition guidance, and medical oversight. We will evaluate retatrutide for inclusion in our program if and when it receives FDA approval.
References
- 1. Jastreboff AM, et al. "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." N Engl J Med. 2023;389(6):514-526.
- 2. Coskun T, et al. "LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss." Cell Metab. 2022;34(9):1234-1247.
- 3. Sanyal AJ, et al. "Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease." Nat Med. 2024;30:2037-2048.
- 4. Rosenstock J, et al. "Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-comparator-controlled, parallel-group, phase 2 trial." Lancet. 2023;402(10401):529-544.
- 5. Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." N Engl J Med. 2021;384(11):989-1002. (STEP 1)
- 6. Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity." N Engl J Med. 2022;387(3):205-216. (SURMOUNT-1)
- 7. Sanyal AJ, et al. "Retatrutide in metabolic dysfunction-associated steatotic liver disease: a randomized phase 2 trial." Nat Med. 2024;30:2037-2048.
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