Retatrutide (LY3437943)
Retatrutide is a triple-receptor agonist (GLP-1, GIP, and glucagon) developed by Eli Lilly. It produced 24.2% body weight loss at 48 weeks in a Phase 2 NEJM trial and 28.7% at 68 weeks in Phase 3 (TRIUMPH-4). No other weight loss compound has matched these numbers in controlled trials.
FormBlends Peptide Context
Reviewed May 14, 2026Retatrutide peptide guide matters because the search behind it is usually practical. The reader is trying to understand peptide therapy, but the safer answer depends on context: diagnosis, medications, labs, dosing, access, price, and follow-up. This page should help narrow the next question before a licensed clinician or qualified provider weighs in.
- Confirm whether the page is discussing approved care, compounded access, off-label use, or research-only context.
- Check the date, evidence quality, safety limits, and whether newer clinical or regulatory updates may change the answer.
- Ask a licensed clinician how the information applies to your history, medications, labs, goals, and risk profile.
Clinical decision snapshot
Retatrutide authority snapshot
Retatrutide is evaluated by mechanism, evidence quality, regulatory status, practical access, and safety questions a licensed clinician would need to review before use.
Evidence signal
Strong human evidence
Regulatory reality
Investigational, not eligible for compounding
Safety screen
Nausea (most common, dose-dependent), Diarrhea, Vomiting should be reviewed in context.
This page currently connects to 12 source-backed evidence items through visible references or structured citation data.
Decision path
What is the supervised-review path for Retatrutide?
Retatrutide should be evaluated by evidence quality, safety status, source quality, dosing context, and whether the goal fits a legitimate clinical pathway. This page is a research and decision aid, not a self-prescribing guide.
- Peptide
- Retatrutide
- Category
- Weight Loss
- Evidence
- Strong human evidence
- FDA status
- Not FDA approved
Step 1
Check evidence level
Retatrutide has the strongest weight loss data of any compound in clinical trials. The Phase 2 NEJM study (n=338) showed 24.2% weight loss at 48 weeks, and the Phase 3 TRIUMPH-4 trial confirmed 28.7% at 68 weeks. A Phase 2a Nature Medicine study demonstrated 82.4% liver fat reduction. Weight loss curves had not plateaued at 48 weeks, suggesting further loss with continued treatment. The data is solid, well-controlled, and consistent across indications.
Review evidenceStep 2
Screen safety context
Nausea (most common, dose-dependent), Diarrhea, Vomiting should be discussed in light of history, dose, and source.
Check side effectsStep 3
Confirm access route
If FormBlends offers access, review the product page and provider pathway before deciding.
Review product accessPipeline watch hub
Retatrutide is a watchlist compound, not a normal access product
Retatrutide deserves deep coverage because it is one of the most important next-generation obesity compounds in late-stage development. It also needs unusually clear language because search demand is running ahead of lawful patient access. The useful page separates triple-agonist science, clinical trial results, approval timing, and gray-market risk.
Decision question for Retatrutide
Is the reader researching future obesity medicine, or trying to find a treatment they can responsibly start now?
Peptide evidence layer
Evidence read
The strongest retatrutide content should distinguish Phase 2 and Phase 3 signals, explain the GLP-1, GIP, and glucagon receptor mix, and compare the mechanism against semaglutide and tirzepatide without implying current routine availability.
Safety watch
Because retatrutide is not a standard approved access pathway, the safety message has to warn against research-only sales, unofficial dosing advice, and products marketed before regulatory review is complete.
Conversion fit
The best conversion bridge is to current supervised options. Readers interested in retatrutide can still compare approved incretin pathways while they follow the pipeline.
Last updated: April 6, 2026
Typical Dosage
Once-weekly subcutaneous injection. Phase 3 doses: 9 mg and 12 mg maintenance, titrated up from 2 mg starting dose. Phase 2 tested 1 mg, 4 mg, 8 mg, and 12 mg doses.
Administration
Subcutaneous injection
Typical Cost
$200-650/month (research suppliers, legally questionable)
FDA Status
Not FDA Approved
Half-Life
Approximately 6 days (terminal elimination), supporting once-weekly dosing
Onset of Action
Tmax 12-72 hours post-injection. Meaningful weight loss begins within first 4 weeks. Body composition changes measurable by 12-24 weeks.
Bioavailability
High following subcutaneous injection. Absorbed via lymphatic system and local blood vessels.
About Retatrutide
Retatrutide (LY3437943) is a 39-amino-acid synthetic peptide developed by Eli Lilly that represents the next evolution in incretin-based obesity treatment. Its CAS number is 2381089-83-2, and its molecular weight is approximately 4,731 Da. What makes retatrutide unique is that it activates three metabolic receptors simultaneously. Semaglutide targets one (GLP-1). Tirzepatide targets two (GLP-1 and GIP). Retatrutide adds the glucagon receptor as a third target, and that addition matters: glucagon agonism drives hepatic energy expenditure, thermogenesis, and fat oxidation on top of the appetite suppression provided by GLP-1 and GIP signaling. The result is the deepest weight loss ever recorded in a clinical trial. The Phase 2 trial, published in the New England Journal of Medicine in June 2023 (PMID: 37366315), enrolled 338 adults with obesity. At 48 weeks, participants on the 12 mg dose lost an average of 24.2% of their body weight, compared to 2.1% on placebo. Critically, the weight loss curves had not plateaued at 48 weeks, suggesting further loss with longer treatment. The first Phase 3 result came from TRIUMPH-4, reported in December 2025, which tested retatrutide in patients with obesity and knee osteoarthritis. The 12 mg dose produced 28.7% mean weight loss (about 71 pounds) at 68 weeks. Beyond weight, retatrutide reduced knee pain scores by 75.8%, and more than 1 in 8 patients became completely free of knee pain. Systolic blood pressure dropped by 14 mmHg, with improvements in cholesterol, hs-CRP, and triglycerides. A Phase 2a study published in Nature Medicine (PMID: 38858523) tested retatrutide in patients with metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD). At 24 weeks, the 12 mg dose reduced liver fat by 82.4%, and 86% of participants achieved normal liver fat levels versus 0% on placebo. This liver data may be as clinically significant as the weight loss data, given that MASLD affects roughly 30% of the global population. Retatrutide is administered as a once-weekly subcutaneous injection, supported by its approximately 6-day half-life. In trials, starting at 2 mg and titrating up over several weeks roughly halved the rate of GI side effects compared to starting at higher doses. The most common side effects are gastrointestinal: nausea, diarrhea, vomiting, and constipation, consistent with the GLP-1 agonist class. As of April 2026, retatrutide is NOT FDA-approved and remains investigational. Seven additional Phase 3 TRIUMPH trials are expected to report results throughout 2026, covering obesity alone, type 2 diabetes, obstructive sleep apnea, chronic low back pain, cardiovascular outcomes, and MASLD. NDA submission is projected for late 2026 or early 2027, with potential FDA approval in mid-to-late 2027. The FDA has issued warning letters to companies selling compounded retatrutide, making clear that any sale outside of clinical trials is currently illegal. Retatrutide does not appear on any compounding category list because it has never been an approved drug.
How Retatrutide Works
Retatrutide is engineered from a GIP peptide backbone to activate three receptors simultaneously. GLP-1 receptor activation suppresses appetite and slows gastric emptying. GIP receptor activation enhances insulin secretion and improves lipid metabolism in adipose tissue. The glucagon receptor component, which separates retatrutide from all approved therapies, drives additional energy expenditure through hepatic thermogenesis, fat oxidation, and lipolysis. The triple mechanism produces weight loss beyond what dual (tirzepatide) or single (semaglutide) agonists achieve.
Receptor targets:
Benefits
- Achieved 24.2% mean weight loss at 48 weeks in Phase 2 (highest dose)
- 28.7% mean weight loss at 68 weeks in Phase 3 TRIUMPH-4
- Reduces liver fat by up to 82.4% in MASLD patients
- Improves glycemic control with clinically meaningful HbA1c reductions
- 72% of participants with prediabetes reverted to normoglycemia
- Reduces systolic blood pressure by up to 14 mmHg
- Reduces knee osteoarthritis pain by up to 75.8%
- Improves triglycerides, non-HDL cholesterol, and hs-CRP
What Does the Research Say?
Retatrutide has the strongest weight loss data of any compound in clinical trials. The Phase 2 NEJM study (n=338) showed 24.2% weight loss at 48 weeks, and the Phase 3 TRIUMPH-4 trial confirmed 28.7% at 68 weeks. A Phase 2a Nature Medicine study demonstrated 82.4% liver fat reduction. Weight loss curves had not plateaued at 48 weeks, suggesting further loss with continued treatment. The data is solid, well-controlled, and consistent across indications.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity -- A Phase 2 Trial
New England Journal of Medicine, 2023 · DOI · PubMed
Up to 24.2% mean body weight loss at 48 weeks with 12 mg dose in 338 adults with obesity; weight loss curves not yet plateaued
Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a phase 2 trial
The Lancet, 2023 · DOI · PubMed
Up to 16.9% weight loss at 36 weeks in T2D patients with clinically meaningful glycemic improvements; 72% with prediabetes reverted to normoglycemia
Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial
Nature Medicine, 2024 · DOI · PubMed
82.4% liver fat reduction at 24 weeks with 12 mg dose; 86% of participants achieved normal liver fat levels vs 0% placebo
Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials
Diabetes, Obesity and Metabolism, 2026 · DOI · PubMed
Design of Phase 3 program with 5,800+ participants across obesity, OSA, and knee OA indications
PubMed evidence trail
Research sources used to frame this page
For Retatrutide, FormBlends checks the page topic against primary trials, systematic reviews, guidelines, and current PubMed-indexed literature where available. These citations are context, not a claim that every study applies to every patient.
Tirzepatide Once Weekly for the Treatment of Obesity
Primary SURMOUNT-1 trial source for tirzepatide weight-loss ranges and tolerability.
PubMed
Continued Treatment With Tirzepatide for Maintenance of Weight Reduction
Used for continuation, stopping, and maintenance questions after initial weight loss.
PubMed
Efficacy of GLP-1 Receptor Agonists on Weight Loss, BMI, and Waist Circumference
A broad meta-analysis anchor for GLP-1 weight-loss effect and class-level comparisons.
PubMed
Discontinuing glucagon-like peptide-1 receptor agonists and body habitus
Used for pages discussing stopping therapy, weight regain, and long-term planning.
PubMed
Potential Side Effects
- Nausea (most common, dose-dependent)
- Diarrhea
- Vomiting
- Constipation
- Decreased appetite
- Transient ALT elevation
- Increased heart rate
- Injection site reactions
Drug Interactions
| Compound | Interaction | Severity |
|---|---|---|
| Insulin and sulfonylureas | Additive hypoglycemia risk. Blood glucose monitoring required and dose reduction of insulin/sulfonylurea may be needed. | major |
| Oral contraceptives | Delayed gastric emptying may reduce absorption. Switch to non-oral contraception or add barrier method during dose escalation. | moderate |
| Other GLP-1 agonists (semaglutide, tirzepatide) | Overlapping mechanisms with no safety data on combination use. Do not combine. | major |
| Warfarin | Potential altered anticoagulant effect. Monitor INR closely when initiating retatrutide. | moderate |
Who Is Retatrutide For?
Women
In Phase 2 trials, women showed greater mean weight reduction than men. Menstrual irregularities reported in early months, typically stabilizing over time. May improve PCOS symptoms through weight loss and improved insulin sensitivity. Oral contraceptive efficacy may be reduced due to delayed gastric emptying. Pregnancy is an absolute contraindication.
Adults Over 50
No retatrutide-specific bone density data yet. Rapid weight loss carries risk of bone mineral density loss and sarcopenia, amplified in adults 50+. Resistance training and high protein intake (1.2-1.6 g/kg/day) strongly recommended. DEXA scanning recommended before and during treatment. Cardiovascular benefits (BP reduction, improved lipids) may be particularly relevant.
Athletes
No specific athletic performance data exists. Lean mass preservation is a concern with rapid weight loss. Resistance training critical to preserve muscle mass. Not currently on WADA prohibited list but could change as the drug progresses toward approval.
Regulatory Status
FDA Approved
No
Compounding Legal
No
2026 HHS Status
Investigational, not eligible for compounding
Retatrutide is an investigational drug that has not been approved by any regulatory agency. The FDA has issued warning letters to companies selling compounded or unapproved retatrutide. It cannot legally be compounded or sold outside of clinical trials.
Last verified: 2026-04-06
Conditions Addressed
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