Retatrutide (LY3437943) hits three receptors instead of one or two. GLP-1 kills appetite. GIP improves insulin sensitivity. Glucagon, the third receptor, is the one nobody expected to matter. It increases energy expenditure and drives liver fat oxidation directly. That calorie-burning effect (thermogenesis) is why retatrutide posted bigger weight loss numbers than tirzepatide (which only hits two of the three). The Phase 2 results in the New England Journal of Medicine were staggering: 24.2% weight loss at the top dose, with half the participants losing 25%+ of body weight. The liver fat data was equally wild, 82.4% reduction. Phase 3 (TRIUMPH program by Eli Lilly) is underway. This is what comes after semaglutide and tirzepatide.
Retatrutide Protocol
Dose: 1mg-12mg per week (titrated up over months) | Frequency: Once weekly | Cycle: Ongoing (not cycled) | Route: SubQ
Start LOW. The Phase 2 trial showed that starting at 2mg caused more nausea than starting at 1mg. Titrate every 4 weeks minimum. The GI side effects at 12mg are significant. Most community protocols target 4-8mg.
Retatrutide Effects
Weight loss (93%). 24.2% body weight loss at the highest dose in 48-week Phase 2 trial. Unprecedented numbers.
Appetite suppression (90%). Triple-receptor activation = the most thorough appetite kill any compound in this class has ever delivered
Liver fat reduction (75%). Up to 82.4% reduction in liver fat at the highest dose. The glucagon receptor activation drives this.
Improved metabolic markers (70%). Blood sugar, insulin sensitivity, and cholesterol all improve. The trifecta your doctor pretends diet alone will fix.
Retatrutide Side Effects
Nausea (60%). Up to 60% at the top dose (12mg). This is why you titrate slowly. Rushing the escalation is asking for a bad time.
Diarrhea (20%). About 1 in 5 people across all dose levels. Usually manageable, not usually the reason people stop.
Vomiting (18%). Hits hardest during dose escalation. Slow. Down.
Constipation (12%). Less common than with sema or tirz. Hydrate.
Decreased appetite (10%). Listed as a side effect in trials. For most people running this, that's literally the point.
Retatrutide Dosing by Use Case
Condition
Dose
Duration
Notes
Weight loss (primary investigation)
1mg to 12mg weekly, titrated
Ongoing, minimum 24 weeks for meaningful results
Start at 1mg for 4 weeks. Increase by 1-2mg every 4 weeks. Phase 2 tested 1mg, 4mg, 8mg, and 12mg maintenance doses. 24.2% weight loss was at 12mg. Most community users target 4-8mg. The 12mg dose works but the GI side effects at that level are serious. Don't rush the titration.
Fatty liver disease (MASLD/NASH)
4-12mg weekly, titrated
24+ weeks
The glucagon receptor is the key here. Retatrutide showed 82.4% liver fat reduction in the Phase 2 MASLD substudy (Sanyal et al., Nature Medicine 2024). No other GLP-1 class compound targets liver fat this aggressively. Tirzepatide and semaglutide reduce liver fat indirectly through weight loss. Retatrutide does it directly. The glucagon receptor tells your liver to burn its own fat.
Metabolic syndrome and insulin resistance
4-8mg weekly
Ongoing
Hitting all three receptors creates broader metabolic improvement than GLP-1 alone or GLP-1/GIP dual agonists. Fasting glucose, A1C, triglycerides, and blood pressure all improved in Phase 2. Lower doses (4mg) may be sufficient for metabolic benefits without targeting maximum weight loss.
After semaglutide or tirzepatide plateau
Start at 1mg, titrate independently
Ongoing
If you've plateaued on semaglutide (GLP-1 only) or tirzepatide (GLP-1/GIP), retatrutide adds the glucagon receptor. The added thermogenic effect may break through a metabolic set point that dual agonists can't reach. Don't start retatrutide at your old semaglutide/tirzepatide dose. Begin the titration from scratch.
Retatrutide Results Timeline
Week 1-4, 1-2mg, calibration phase: Appetite may shift slightly. The GLP-1 receptor is engaging first. Mild nausea is common. This dose is about tolerance, not results. Some people feel nothing yet. That's normal. The glucagon receptor doesn't fully activate until higher doses.
Week 4-12, 4mg, triple activation begins: The glucagon receptor starts contributing at this dose. You start burning more calories at rest. Appetite suppression deepens. 2-5% body weight loss is typical by week 12. You may notice feeling warmer than usual. That's thermogenesis from the glucagon component.
Week 12-24, 8mg, peak weight loss rate: Fastest rate of weight loss. The triple-receptor effect is in full swing. Liver fat is dropping measurably. GI side effects are real but manageable. Watch protein intake aggressively. At this rate of weight loss, muscle preservation requires deliberate effort.
Week 24-48, 8-12mg, maintenance and consolidation: Weight loss continues but decelerates toward a new set point. The Phase 2 trial ran 48 weeks. Half the participants on the highest dose lost 25%+ of body weight by this point. No published data yet on what happens after stopping, but based on semaglutide and tirzepatide precedent, expect this to be a long-term commitment.
Frequently Asked Questions About Retatrutide
What is retatrutide?
Retatrutide (LY3437943) is a triple hormone receptor agonist developed by Eli Lilly. It activates three receptors simultaneously: GIP, GLP-1, and glucagon. Semaglutide (Ozempic/Wegovy) hits one receptor (GLP-1). Tirzepatide (Mounjaro/Zepbound) hits two (GLP-1 + GIP). Retatrutide adds the glucagon receptor, which increases energy expenditure and drives liver fat oxidation. The Phase 2 trial published in the New England Journal of Medicine showed 24.2% body weight loss at the highest dose over 48 weeks, the biggest weight loss number anyone's seen in a trial. Period.
What is the retatrutide dosage schedule?
Start at 1mg once weekly for 4 weeks. Increase by 1-2mg every 4 weeks. The Phase 2 trial tested maintenance doses of 1mg, 4mg, 8mg, and 12mg. Starting at 2mg caused more nausea than starting at 1mg in the trial, so the lower entry point matters. Most community protocols target 4-8mg weekly as the sweet spot between efficacy and tolerability. 12mg produced the highest weight loss but also 60% nausea rates.
What are the side effects of retatrutide?
Nausea (up to 60% at 12mg), diarrhea (20%), vomiting (18%), constipation (12%), and decreased appetite (10%). GI side effects are dose-dependent and worst during titration. They typically settle 1-2 weeks after each dose increase. The nausea rates are higher than semaglutide or tirzepatide because the glucagon receptor adds its own GI effects on top of the GLP-1 component. Slow titration is non-negotiable. Serious adverse events were rare in Phase 2.
How does retatrutide compare to tirzepatide?
Tirzepatide hits GLP-1 + GIP (two receptors). Retatrutide hits GLP-1 + GIP + glucagon (three receptors). The glucagon receptor is the differentiator. It increases energy expenditure (thermogenesis) and drives liver fat oxidation directly. Phase 2 data: retatrutide 24.2% weight loss at 48 weeks vs tirzepatide 22.5% at 72 weeks in SURMOUNT-1. Retatrutide also showed 82.4% liver fat reduction, dramatically more than tirzepatide. GI side effects are worse with retatrutide at higher doses. No head-to-head trial exists yet.
Is retatrutide FDA-approved?
No. As of September 2026, retatrutide is not FDA-approved for any indication. Phase 3 trials (the TRIUMPH program) are underway for obesity and type 2 diabetes. The Phase 2 data was published in the New England Journal of Medicine in June 2023. A separate Phase 2 trial for fatty liver disease (MASLD) was published in Nature Medicine in 2024. FDA approval depends on TRIUMPH results. Compounded or research-grade retatrutide exists in the market but is not a regulated pharmaceutical product.
How do you reconstitute retatrutide?
For a 10mg lyophilized vial: add 2mL of bacteriostatic water. That gives you 5mg per mL. For a 1mg dose, draw 20 units on a U-100 insulin syringe. For 4mg, draw 80 units. For 8mg, you need 1.6mL (160 units), so you may need a larger syringe or split into two draws. Aim the water at the glass wall, not directly on the powder. Swirl gently. Never shake. Refrigerate after reconstitution. Use within 28 days.
Why does the glucagon receptor matter?
Glucagon is typically associated with raising blood sugar, which sounds counterproductive in an obesity drug. But when combined with GLP-1 and GIP, the glucagon receptor activation does something different: it increases energy expenditure (your body burns more calories at rest) and tells your liver to burn its stored fat. This thermogenic effect is why retatrutide produces bigger weight loss numbers than tirzepatide. You're not just eating less. You're burning more. The liver fat data (82.4% reduction) comes almost entirely from this pathway.
Can you switch from semaglutide or tirzepatide to retatrutide?
People do, but don't carry your dose over. Start retatrutide from scratch at 1mg regardless of what you were on before. The glucagon receptor is new to your system and needs its own titration. Some people switch because they've plateaued on semaglutide or tirzepatide. The added receptor gives the metabolic system a new stimulus. Wait at least 2 weeks after your last semaglutide/tirzepatide dose before starting retatrutide (both have ~1 week half-lives, so 2 weeks gives reasonable washout).
Evidence
Emerging evidence. Phase 2 trial published in NEJM showed 24.2% body weight loss at the highest dose over 48 weeks, the biggest number any obesity compound has posted. Phase 3 trials (TRIUMPH program) are underway. Also showed 82.4% liver fat reduction. Not yet approved, but the data broke the internet for a reason.
Approval status: Not approved. Phase 3 (TRIUMPH) ongoing.
References
Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med, 2023. PMID 37366315
Sanyal AJ, Bedossa P, Engel SS, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med, 2024. PMID 38858523
Doggrell SA. Is retatrutide (LY3437943), a GLP-1, GIP, and glucagon receptor agonist a step forward in the treatment of diabetes and obesity? Expert Opin Investig Drugs, 2023. PMID 37086147
Doggrell SA. Retatrutide showing promise in obesity (and type 2 diabetes). Expert Opin Investig Drugs, 2023. PMID 37947489
Ganamurali N, Jain R, Nithya V, et al. The Triple-Agonist Revolution: Retatrutide and the Paradigm Shift in Multi-Hormonal Pharmacotherapy for Obesity and Cardiometabolic Comorbidities. Clin Pharmacol Drug Dev, 2026. PMID 41545327
Storage
Lyophilized: Refrigerate at 2-8C. Stable for 6+ months sealed.
Reconstituted: Refrigerate. Use within 28 days.
Water: Bacteriostatic water, 2mL per 10mg vial for compounded versions.
Needle: 30-31 gauge, 0.5 inch for subcutaneous injection
These statements have not been evaluated by the FDA. This content is for educational purposes only. Consult a healthcare professional before starting any protocol. vialprep sells injection supplies, not compounds.
