⚠️ Investigational Medication
Retatrutide is not yet FDA-approved. It is currently in Phase 3 clinical trials. The information on this page is based on published trial data and may change as additional results become available. Do not use this information to make treatment decisions — discuss all options with your healthcare provider.
What is Retatrutide?
Retatrutide (LY3437943) is a first-in-class investigational medication developed by Eli Lilly that simultaneously activates three hormone receptors involved in metabolism and weight regulation:
- GLP-1 (glucagon-like peptide-1) receptor — Suppresses appetite, enhances insulin secretion, slows gastric emptying. The same target as Ozempic and Wegovy.
- GIP (glucose-dependent insulinotropic polypeptide) receptor — Enhances insulin response, improves fat metabolism. Also targeted by Mounjaro and Zepbound (along with GLP-1).
- Glucagon receptor — The breakthrough addition. Increases energy expenditure through thermogenesis, promotes fat oxidation, and enhances liver fat reduction. This is what makes retatrutide unique.
By engaging all three receptors, retatrutide addresses obesity through more pathways than any existing medication — reducing food intake (GLP-1/GIP), improving metabolic signaling (GIP), AND actively increasing the body's calorie-burning capacity (glucagon).
💡 Why the Glucagon Receptor Matters
Existing GLP-1 drugs primarily work by making you eat less. Retatrutide's glucagon receptor activation adds a fundamentally different mechanism: it tells your body to burn more energy, even at rest. Glucagon promotes thermogenesis (heat production from fat), increases fat oxidation in the liver, and boosts resting energy expenditure. This "burn more" effect on top of the "eat less" effect is why retatrutide achieves weight loss results that exceed any approved medication.
How Does Retatrutide Work?
Retatrutide is a single molecule engineered to activate three distinct receptor pathways simultaneously. Here's how each contributes:
1. GLP-1 Receptor: Appetite Suppression
Like semaglutide (Ozempic/Wegovy), retatrutide activates GLP-1 receptors in the brain and gut. This reduces hunger signals, slows stomach emptying so you feel fuller longer, and enhances glucose-dependent insulin secretion to improve blood sugar control.
2. GIP Receptor: Metabolic Enhancement
Like tirzepatide (Mounjaro/Zepbound), retatrutide also activates GIP receptors. GIP signaling enhances the insulin response to meals, improves fat tissue metabolism, and may help preserve lean muscle mass during weight loss — a critical advantage over simple calorie restriction.
3. Glucagon Receptor: Thermogenesis & Fat Burning
This is retatrutide's unique advantage. Glucagon receptor activation promotes:
- Thermogenesis — Increases the body's heat production, burning additional calories even at rest
- Hepatic fat oxidation — Stimulates the liver to break down stored fat for energy
- Increased energy expenditure — Raises the basal metabolic rate, countering the metabolic slowdown that typically accompanies weight loss
- Liver fat reduction — Phase 2 data showed dramatic reductions in liver fat, relevant for MASH/fatty liver disease
💡 The Evolution: Single → Dual → Triple
Generation 1: Semaglutide (Ozempic/Wegovy) — GLP-1 only → ~15-17% weight loss.
Generation 2: Tirzepatide (Mounjaro/Zepbound) — GLP-1 + GIP → ~20-25% weight loss.
Generation 3: Retatrutide — GLP-1 + GIP + Glucagon → ~24%+ weight loss, with enhanced fat burning.
Each generation adds a new mechanism, yielding progressively greater results.
Phase 3 Trial Results
Retatrutide has been studied in both Phase 2 and Phase 3 clinical trials with striking results:
TRIUMPH-1 (Phase 3, May 2026)
TRIUMPH-1 is the pivotal obesity trial. It enrolled 2,339 adults with obesity or overweight and at least one weight-related condition, without diabetes. Lilly reported topline results on May 21, 2026 (Lilly press release):
- Average weight loss at 80 weeks: 19.0% (47.2 lbs) on 4 mg, 25.9% (64.4 lbs) on 9 mg, and 28.3% (70.3 lbs) on 12 mg, versus 2.2% (5.5 lbs) on placebo
- Two-year extension: in a pre-specified extension for people with a BMI of 35 or higher, participants who stayed on 12 mg reached an average 30.3% (85.0 lbs) weight loss at 104 weeks
- Discontinuation for adverse events: 4.1% (4 mg), 6.9% (9 mg), 11.3% (12 mg), and 4.9% (placebo)
TRIUMPH-2 and TRIUMPH-3 (Phase 3, July 2026)
On July 23, 2026, Lilly reported positive results from two more pivotal trials and said it plans to submit a Biologics License Application (BLA) to the FDA in the first quarter of 2027 (Lilly press release):
- TRIUMPH-2 (1,152 adults with type 2 diabetes and obesity or overweight): 20.8% (49.6 lbs) weight loss on 12 mg at 80 weeks versus 4.0% on placebo, with A1C reductions of 1.4 to 1.6 percentage points across doses
- TRIUMPH-3 (1,949 adults with severe obesity and established cardiovascular disease): 22.6% (55.8 lbs) weight loss on 12 mg at 80 weeks versus 3.2% on placebo
TRIUMPH-4 (Phase 3, December 2025)
The first Phase 3 readout, reported December 11, 2025, studied 445 adults with obesity or overweight and knee osteoarthritis (Lilly press release):
- Average weight loss: 71.2 lbs (28.7% of body weight) on 12 mg at 68 weeks, versus 2.1% on placebo
- Knee pain (WOMAC) fell by up to 4.5 points (75.8%); 12.0% of participants on 12 mg (14.1% on 9 mg) were pain-free at week 68
- Safety profile consistent with earlier trials; most adverse events were GI-related and manageable
TRANSCEND-T2D-1 (Phase 3, published in The Lancet, June 2026)
The first peer-reviewed Phase 3 publication appeared in The Lancet in June 2026. In 537 adults with type 2 diabetes not controlled by diet and exercise, retatrutide 12 mg lowered A1C by 1.94 percentage points at 40 weeks (placebo: 0.81) and reduced body weight by 15.3% (placebo: 2.6%) (Bajaj et al., Lancet 2026).
Phase 2 Trial (Published in NEJM, 2023)
The pivotal Phase 2 trial enrolled 338 adults with obesity and demonstrated:
- Up to 24.2% body weight loss at 48 weeks (12 mg dose)
- Over 25% of participants lost more than 30% of their body weight
- Dramatic reductions in liver fat content
- Improvements in blood sugar, cholesterol, and blood pressure
Ongoing Phase 3 Program
Eli Lilly has a comprehensive Phase 3 program with 8 total TRIUMPH trials studying retatrutide across multiple indications:
- TRIUMPH-1: Obesity / weight management (results reported May 2026)
- TRIUMPH-2: Obesity with type 2 diabetes (results reported July 2026)
- TRIUMPH-3: Severe obesity with established cardiovascular disease (results reported July 2026)
- TRIUMPH-4: Obesity with knee osteoarthritis (results reported Dec 2025)
- TRIUMPH-5: MASH (metabolic dysfunction-associated steatohepatitis)
- Additional trials studying cardiovascular outcomes and other comorbidities
The four core obesity trials are complete. Lilly plans to submit the BLA to the FDA in the first quarter of 2027. The remaining trials continue to read out through 2026 and 2027.
Retatrutide vs. Existing Medications
How does retatrutide stack up against the current generation of weight loss and diabetes medications?
| Feature | Retatrutide | Ozempic | Mounjaro | Zepbound |
|---|---|---|---|---|
| Active Ingredient | Retatrutide | Semaglutide | Tirzepatide | Tirzepatide |
| Manufacturer | Eli Lilly | Novo Nordisk | Eli Lilly | Eli Lilly |
| Receptors | GLP-1 + GIP + Glucagon | GLP-1 only | GLP-1 + GIP | GLP-1 + GIP |
| Type | Triple agonist | Single agonist | Dual agonist | Dual agonist |
| Frequency | Once weekly | Once weekly | Once weekly | Once weekly |
| Avg Weight Loss | ~28% / 70 lbs (80 wk) | ~15% / 35 lbs | ~21% / 52 lbs | ~22% / 55 lbs |
| FDA Approved | Not yet (Phase 3) | Yes (diabetes) | Yes (diabetes) | Yes (weight loss) |
| Indication | Obesity, T2D (investigational) | Type 2 diabetes | Type 2 diabetes | Chronic weight mgmt |
| Thermogenesis | Yes (glucagon) | No | No | No |
| Cost/Month | TBD | $935 | $1,023 | $1,060 |
Weight loss data from respective Phase 3 trials at highest approved/studied doses. Retatrutide data from TRIUMPH-1 (12 mg, 80 weeks). Prices are average U.S. cash prices without insurance (GoodRx, February 2026). Retatrutide pricing not yet announced.
vs. Ozempic
Ozempic targets only GLP-1. Retatrutide adds GIP and glucagon receptors, producing roughly 60% more weight loss and active fat-burning effects Ozempic doesn't have.
vs. Mounjaro
Mounjaro shares GLP-1 and GIP targeting with retatrutide but lacks the glucagon component. Retatrutide adds thermogenesis and enhanced liver fat reduction on top of Mounjaro's dual mechanism.
vs. Zepbound
Zepbound is the same molecule as Mounjaro, approved for weight loss. Retatrutide's glucagon activation provides additional calorie burning that Zepbound cannot achieve.
vs. Wegovy
Wegovy is high-dose semaglutide for weight loss. Retatrutide's triple mechanism produces significantly more weight loss (~28% vs ~15-17%) and actively boosts metabolism.
Side Effects of Retatrutide
Retatrutide's side effect profile in clinical trials is similar to other GLP-1 class medications, with gastrointestinal symptoms being the most common. Most side effects are mild to moderate and tend to improve over time.
Common Side Effects (reported in trials)
- Nausea — Up to 45% of participants; most common during dose escalation
- Diarrhea — Up to 28%; typically mild and self-limiting
- Vomiting — Up to 22%; decreases with continued treatment
- Constipation — Up to 15%; manageable with fiber and hydration
- Decreased appetite — Expected pharmacologic effect; not necessarily adverse
- Injection site reactions — Mild redness or discomfort at injection site
Potential Serious Risks (monitored in trials)
- Pancreatitis — As with all GLP-1 class medications; patients are monitored
- Gallbladder events — Rapid weight loss increases gallstone risk
- Heart rate increase — Slight elevation observed, likely related to glucagon activity
- Thyroid C-cell tumors — Observed in animal studies with GLP-1 agonists; clinical significance in humans unclear
- Hypoglycemia — Risk increases when combined with insulin or sulfonylureas
💡 GI Side Effects: Manageable with Titration
Like other incretin-based medications, retatrutide uses a slow dose-escalation schedule. Starting at a low dose and increasing gradually every 4 weeks allows the body to adjust and significantly reduces the severity and frequency of nausea, vomiting, and diarrhea. In clinical trials, most GI side effects occurred during the first few weeks of each dose increase and resolved without treatment discontinuation.
Who Might Be Eligible for Retatrutide?
While retatrutide is not yet approved, clinical trials provide insight into who may eventually be candidates:
Likely Eligibility (based on trial enrollment criteria)
- Adults with obesity — BMI ≥ 30
- Adults who are overweight — BMI ≥ 27 with at least one weight-related comorbidity (type 2 diabetes, hypertension, dyslipidemia, sleep apnea)
- Adults with type 2 diabetes — As an adjunct to diet and exercise
- Adults with MASH — Metabolic dysfunction-associated steatohepatitis (fatty liver disease)
- Adults with obesity-related osteoarthritis — Based on TRIUMPH-4 results showing pain relief
Likely Contraindications
- Personal or family history of medullary thyroid carcinoma (MTC)
- Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
- History of severe pancreatitis
- Pregnancy or breastfeeding
- Known hypersensitivity to any component
⚠️ Not Yet Available by Prescription
Retatrutide cannot currently be prescribed or purchased. It is only available through clinical trial participation. Be wary of any online sellers claiming to offer retatrutide — these products are unregulated and potentially dangerous. On August 12, 2026, Lilly filed six lawsuits against U.S. sellers of black-market retatrutide and said no regulator anywhere has approved any retatrutide product for human use (Lilly press release). The legitimate medication will only be available after FDA approval through licensed pharmacies.
Retatrutide FAQ
When will retatrutide be available?
Retatrutide is still investigational. The four core Phase 3 obesity trials (TRIUMPH-1 through TRIUMPH-4) reported positive results between December 2025 and July 2026. On July 23, 2026, Eli Lilly said it plans to submit a Biologics License Application (BLA) to the FDA in the first quarter of 2027 (Lilly press release). FDA review usually takes about 10 to 12 months after submission, so approval and availability are not expected before late 2027 or 2028.
How much will retatrutide cost?
Pricing has not been announced. Given that Mounjaro/Zepbound (tirzepatide) costs approximately $1,000-$1,100/month without insurance, retatrutide may be priced similarly or higher as a next-generation medication. Insurance coverage and manufacturer savings programs will significantly impact out-of-pocket costs.
Is retatrutide better than Mounjaro?
Based on clinical trial data, retatrutide produces greater weight loss (~28% at 80 weeks vs ~21-22% of body weight) than tirzepatide (Mounjaro/Zepbound). The glucagon receptor activation provides additional thermogenic and fat-burning effects. However, direct head-to-head trials have not been conducted, and individual responses vary. "Better" also depends on tolerability, cost, and individual health goals.
Can I get retatrutide now through clinical trials?
Some Phase 3 trials may still be enrolling participants. Visit ClinicalTrials.gov and search for "retatrutide" to find active studies near you. Eligibility criteria vary by trial.
Will retatrutide work for people who didn't respond to Ozempic or Mounjaro?
Possibly. Because retatrutide activates an additional receptor (glucagon) that existing medications don't target, it may benefit patients who had suboptimal responses to GLP-1-only or GLP-1/GIP dual agonists. The glucagon-driven thermogenesis is a fundamentally different weight loss mechanism. However, this hasn't been specifically studied in clinical trials.
Is retatrutide an injection?
Yes. Like Ozempic, Wegovy, Mounjaro, and Zepbound, retatrutide is administered as a once-weekly subcutaneous injection. An oral formulation has not been announced.
The Future of Obesity Treatment
Retatrutide represents the next frontier in obesity pharmacotherapy. Its triple-agonist approach signals a broader trend: treating obesity as a complex metabolic disease requiring multi-targeted intervention.
Key developments to watch:
- Full Phase 3 program readouts (2026) — Results across obesity, diabetes, MASH, sleep apnea, and osteoarthritis will define retatrutide's clinical profile
- Cardiovascular outcome data — Whether retatrutide matches or exceeds the CV benefits seen with semaglutide in the SELECT trial
- Long-term durability — How well weight loss is maintained beyond 48 weeks
- Muscle preservation — Whether the glucagon component helps preserve lean mass during rapid weight loss
- Combination approaches — Future drugs may add even more receptor targets for further metabolic improvement
- Insurance coverage — As evidence grows for obesity medications reducing overall healthcare costs, coverage is expected to expand
If approved, retatrutide would be the most potent weight loss medication ever available — and a clear signal that obesity treatment is entering a new era of multi-mechanism pharmacotherapy.
Last reviewed: September 2026 by the thrive.md Clinical Advisory Team
Frequently asked questions
What is retatrutide?
Retatrutide (LY3437943) is a first-in-class triple hormone receptor agonist developed by Eli Lilly. It activates three receptors simultaneously: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon receptors. This triple mechanism is designed to provide superior weight loss and metabolic benefits compared to existing single (semaglutide) or dual (tirzepatide) agonists.
How is retatrutide different from Ozempic or Mounjaro?
Ozempic (semaglutide) targets only the GLP-1 receptor. Mounjaro (tirzepatide) targets two receptors: GLP-1 and GIP. Retatrutide targets all three: GLP-1, GIP, AND glucagon receptors. The addition of glucagon receptor activation promotes thermogenesis (heat production) and fat oxidation, potentially leading to greater weight loss. In the Phase 3 TRIUMPH-1 trial, retatrutide 12 mg produced an average 28.3% (70.3 lbs) weight loss at 80 weeks and 30.3% (85.0 lbs) at 104 weeks in an extension for people with a BMI of 35 or higher, exceeding results seen with either Ozempic or Mounjaro.
What are the side effects of retatrutide?
Retatrutide has a similar gastrointestinal side effect profile to other GLP-1 medications. The most common side effects in clinical trials include nausea (up to 45%), diarrhea (up to 28%), vomiting (up to 22%), constipation, and decreased appetite. Most side effects are mild to moderate and tend to improve over time with continued use.
How much weight can you lose on retatrutide?
In the Phase 3 TRIUMPH-1 trial (May 2026), participants on retatrutide 12 mg lost an average of 28.3% of body weight (70.3 lbs) at 80 weeks and 30.3% (85.0 lbs) at 104 weeks in an extension for people with a BMI of 35 or higher. In TRIUMPH-4 (December 2025), adults with obesity and knee osteoarthritis lost an average of 28.7% (71.2 lbs) at 68 weeks on 12 mg. In the earlier Phase 2 trial, participants lost up to 24.2% of body weight at 48 weeks. These results exceed those seen with any currently approved weight loss medication.
Who might be eligible for retatrutide?
While retatrutide is not yet approved, clinical trials have enrolled adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity. Separate trials are studying retatrutide for type 2 diabetes, obstructive sleep apnea, osteoarthritis, and metabolic dysfunction-associated steatohepatitis (MASH). Eligibility criteria for the eventual approved medication will be determined by the FDA.