Phase 3 Data — March 2026
Retatrutide 2026:
The Complete Guide
Triple GLP-1/GIP/Glucagon agonist with 28.7% average body weight reduction in TRIUMPH Phase 3 trials — the highest number ever recorded for a pharmacological weight loss intervention. Here is everything you need to know.
01
What Is Retatrutide?
Retatrutide (LY3437943) is an investigational peptide developed by Eli Lilly that simultaneously activates three receptors: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. This triple agonism is what makes it categorically different from every weight loss compound that came before it.
Semaglutide works on one receptor (GLP-1). Tirzepatide works on two (GLP-1 + GIP). Retatrutide works on all three — and that additional glucagon receptor activation is the key differentiator. Glucagon receptor agonism directly increases energy expenditure and hepatic fat burning in ways that GLP-1 and GIP cannot replicate, explaining the dramatically superior weight loss outcomes seen in TRIUMPH trials.
The compound was first reported in Phase 1 data in 2023 and has since completed Phase 2 and entered Phase 3 trials (TRIUMPH program) covering obesity, type 2 diabetes, cardiovascular outcomes, and liver disease (MASH).
02
TRIUMPH Phase 3 Results: All Data Consolidated
The TRIUMPH program is Eli Lilly's Phase 3 clinical trial series for retatrutide across multiple indications. Here is every major data readout to date:
TRIUMPH-4 (Obesity)
28.7% average body weight reductionPrimary obesity trial — the headline number
Phase 2 Obesity
24.2% average body weight reductionConfirmed in earlier study
TRIUMPH Diabetes (March 2026)
Phase 3 diabetes trial clearedLate-stage data released March 19, 2026
MASH (Liver Disease)
Significant MASH resolution vs. placeboBroadening the clinical picture beyond obesity
03
Retatrutide vs. Tirzepatide vs. Semaglutide
The three GLP-class compounds represent a clear generational progression. Each adds a receptor, and each addition meaningfully increases efficacy.
| Compound | Receptors | Avg. Weight Loss | FDA Status | Key Downside |
|---|---|---|---|---|
| Semaglutide | GLP-1 | 13.7–14.9% | Approved (Wegovy) | Lowest efficacy of the three |
| Tirzepatide | GLP-1 + GIP | 20.2–22.5% | Approved (Zepbound) | More expensive, limited insurance |
| Retatrutide | GLP-1 + GIP + Glucagon | 24.2–28.7% | Phase 3 (~2027) | Dysesthesia, not yet approved |
Note: weight loss percentages from separate trials with different populations and durations. Direct head-to-head data pending TRIUMPH completion.
04
Side Effects — Including the Dysesthesia Signal
Retatrutide shares the GI side effect profile of all GLP-1 agonists: nausea, vomiting, diarrhea, and constipation during dose escalation. These are dose-dependent and largely resolve after the escalation phase. Standard slow titration protocol mitigates most GI effects.
The unique signal: dysesthesia. Unlike semaglutide and tirzepatide, retatrutide produced dysesthesia (abnormal skin sensations including tingling, numbness, and prickling) in 8.8%–20.9% of subjects across dose groups in Phase 2. This is attributed to the glucagon receptor component and is not seen with the other GLP-class compounds. In most cases it was mild to moderate and resolved with dose reduction.
Nausea / Vomiting
Common — GI class effect
Slow escalation protocol
Dysesthesia
8.8–20.9% of patients
Dose reduction, usually resolves
Constipation
Common
Fiber, hydration, time
Muscle loss (lean mass)
Present — dose dependent
Resistance training mandatory
05
FDA Approval Timeline — What to Expect
As of March 2026, retatrutide has not received FDA approval for any indication. The TRIUMPH obesity Phase 3 program is the primary pathway to approval. Based on current trial progress and standard FDA review timelines, the earliest realistic approval date for obesity is Q3–Q4 2027.
The diabetes Phase 3 trial cleared its first readout in March 2026 — a significant milestone that increases confidence in the regulatory pathway, but does not accelerate the obesity approval timeline meaningfully.
Key events to watch: TRIUMPH primary obesity endpoint data (expected late 2026), FDA NDA submission (2027), cardiovascular outcomes trial data (TRIUMPH-CV, ongoing).
06
How to Access Retatrutide in 2026
Before FDA approval, retatrutide is available in lyophilized research peptide format from licensed vendors. This is the same format used for all research peptides — reconstituted with bacteriostatic water and administered subcutaneously per the researcher's protocol.
Premium pharmaceutical-grade retatrutide is available with full certificate of analysis verification. The available formats (10mg, 30mg, 60mg) align with the dose ranges studied in TRIUMPH trials.
For context while waiting: tirzepatide is the current best-approved option at 22.5% weight loss and is available now.
Read the full GLP-1 comparison guide →07
Frequently Asked Questions
What is retatrutide?
Retatrutide is a triple agonist developed by Eli Lilly that activates GLP-1, GIP, and glucagon receptors simultaneously. Phase 3 TRIUMPH trials show 28.7% average body weight reduction — the highest ever recorded for a pharmacological weight loss intervention.
How does retatrutide compare to tirzepatide?
Retatrutide outperforms tirzepatide on weight loss (28.7% vs 22.5%) due to its additional glucagon receptor activation. However, retatrutide introduces a unique side effect — dysesthesia — not seen with tirzepatide, and remains unapproved as of 2026.
When will retatrutide be FDA approved?
Earliest Q3 2027 based on current Phase 3 timelines and standard FDA review periods. No submission date has been announced by Eli Lilly.
What should I use while waiting for retatrutide?
Tirzepatide is the strongest currently available option at 22.5% average body weight reduction. Semaglutide is an alternative at 14.9% for those who prefer the more established safety record.
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