retatrutide

the most potent weight loss drug ever tested. 24.2% in phase 2, then 28.3% in TRIUMPH-1 phase 3, 30.3% at two years. not approved yet.

tier S · weight loss · 28.3% TRIUMPH-1 phase 3

verdict

the triple agonist with the highest weight-loss number ever recorded in a phase 3 obesity trial. not FDA-approved yet.

if you're asking whether retatrutide is worth waiting for — TRIUMPH-1 (May 2026), the pivotal phase 3 obesity trial, hit 28.3% mean weight loss at 12 mg over 80 weeks, rising to 30.3% (85 lbs) at 104 weeks in the BMI-≥35 extension. that's the deepest phase 3 obesity number on record. FDA filing is post-TRIUMPH. the approval call belongs to the full phase 3 package, not to gray-market reports.

if you're asking about gray-market retatrutide — pre-approval, peptide-vendor channel only. no GMP, no FDA-reviewed label, no controlled dose-response data for the population using it. community reports describe sharper food aversion than tirzepatide and faster onset. the unknowns are sourcing, identity, concentration, and a nerve-sensation side effect (dysesthesia, tingling or burning in the hands and feet), reported in 12.5% of people at 12 mg in the phase 3 trial (TRIUMPH-1), higher in the smaller phase 2 (~21%), and echoed in community reports.

if you came in worried about the glucagon arm — the glucagon receptor agonism is the wildcard. resting energy expenditure rises about 6%, heart rate ticks up. trial data through 12 mg shows no clinical surprise. the long-term cardiovascular and metabolic questions stay open until the post-approval datasets accumulate.

based on published evidence and disclosed clinical practice. not medical advice. dose and protocol conversations belong with a clinician.

why S-tier

now that the pivotal phase 3 obesity trial has read out (TRIUMPH-1: 28.3% weight loss at 12mg over 80 weeks, 30.3% at two years), reta has the strongest published obesity-drug efficacy in the catalog. Bariatric-surgery territory from a weekly shot. triple receptor mechanism adds glucagon agonism on top of tirz's dual mechanism, which pushes lipolysis and energy expenditure. S-tier based on phase 3 efficacy, but with meaningful open questions on safety and no announced approval date.

the core tension

24.2% in phase 2 was the first shock. 28.3% at 80 weeks (30.3% at two years) in TRIUMPH-1, the pivotal phase 3 obesity trial, was the confirmation. Still not approved. The story here is less about the drug and more about what happens to the obesity market when it lands.

what it is

A 39-amino-acid investigational triple agonist. Activates GLP-1, GIP, and glucagon receptors at once. Eli Lilly internal code LY3437943. Direct successor to tirzepatide. The novel piece is glucagon agonism, yes, glucagon, the hormone that raises blood sugar. Paired with GLP-1 and GIP it drives lipolysis and resting energy expenditure without hyperglycemia.

what it does

The GLP-1 and GIP arms deliver tirzepatide-grade satiety and insulin effects. The glucagon arm adds a roughly 6% bump in resting energy expenditure. TRIUMPH-1 (phase 3, May 2026): 28.3% mean weight loss at 12mg over 80 weeks (average 70.3 pounds), rising to 30.3% (85 pounds) at 104 weeks in the BMI-≥35 extension. The nested knee-OA and OSA basket results have not been released yet. Phase 2 MASH data: greater than 80% relative liver fat reduction.

origin

Built inside Lilly's incretin pipeline as the step after tirzepatide. Phase 2 results landed in NEJM in June 2023. The TRIUMPH registrational program runs four phase 3 trials with nested OSA and OA protocols, 5,800+ participants, five doses. TRIUMPH-1, the pivotal obesity trial, read out May 2026. TRIUMPH-2 (type 2 diabetes) and TRIUMPH-3 (cardiovascular disease) are expected later in 2026. Lilly has not announced an NDA filing date. FDA timing depends on the full phase 3 safety package.

why researchers are interested

Bariatric-surgery weight loss from a weekly shot. The peptide community treated reta as the next-generation product the moment the NEJM paper dropped. Gray-market vendors were listing it within 18 months. Reports describe sharper food aversion than tirzepatide, faster onset, and the novel side effect (dysesthesia, tingling in extremities) at rates near the trial incidence (12.5% at 12 mg in TRIUMPH-1, higher in the smaller phase 2).

does it work

Yes on efficacy, with caveats. Phase 3 data is real now, not a projection. 28.3% weight loss at 80 weeks, climbing to 30.3% at two years, is the deepest number any obesity drug has produced in a phase 3 obesity trial to date. Open questions: dysesthesia incidence (12.5% at 12 mg), heart-rate elevation from the glucagon arm, long-term safety, and an AE-driven discontinuation rate of 11.3% at the top dose. The current record supports high efficacy and unresolved safety. The approval call belongs after the full phase 3 package, not the gray market.

claims vs the data

• most effective weight loss drug ever — supported — TRIUMPH-1 (May 2026): 28.3% at 80 weeks, 30.3% at two years. deepest phase 3 obesity number to date.
• matches bariatric surgery results — partially true — weight loss magnitude comparable at 1 year. long-term durability and metabolic improvements still being measured.
• also treats knee osteoarthritis — unverified — knee-OA is a basket trial nested in TRIUMPH-1. Lilly says those results will be released separately; no WOMAC data has been published yet.
• glucagon agonism improves metabolism — supported — resting energy expenditure elevated. hepatic fat oxidation accelerated. liver fat reduction striking in MASH studies.
• better tolerated than tirz — contradicted — TRIUMPH-1: 11.3% AE discontinuation at 12mg vs 4.9% placebo, plus a novel dysesthesia signal (12.5% at 12mg). not better-tolerated than tirz.
• will be approved in 2026 — weak — Lilly has not confirmed an NDA filing date. regulatory timing depends on the full phase 3 package.
• safer than older weight loss drugs — unverified — no long-term safety data. the TRIUMPH program is still reading out.
• retatrutide is basically already approved — overreach — The phase-2 efficacy signal is extraordinary and phase-3 registries are active, but registries are not approvals and phase-2 safety is not the same as a mature postmarketing record. The correct frame is high ceiling, unfinished file.

key facts

• molecular formula: C₂₁₉H₃₃₈N₅₀O₆₅S
• molecular weight: 4731.4 g/mol
• amino acids: 39
• half-life: ~6 days
• type: GIP/GLP-1/glucagon triple agonist
• CAS: 2381089-83-2
• 28.3% avg weight loss, 80wk (TRIUMPH-1)
• 30.3% avg weight loss, 104wk extension
• 45.3% hit ≥30% weight loss (12mg)
• 85 lb avg lost at 104wk (12mg)

frequently asked questions

What is retatrutide?

Retatrutide is an experimental triple agonist peptide targeting GLP-1, GIP, and glucagon receptors. Developed by Eli Lilly, it is in ongoing Phase 3 clinical trials for obesity and related metabolic conditions as of May 2026.

What does retatrutide do?

Retatrutide combines the appetite-suppressing and glucose-regulating effects of GLP-1/GIP with glucagon-receptor activation, which increases energy expenditure. Phase 2 trial data showed 24.2% body weight loss at 48 weeks. TRIUMPH-1, the pivotal phase 3 obesity trial, reported 28.3% mean weight loss at 12 mg over 80 weeks (May 2026), rising to 30.3% at 104 weeks in the BMI-≥35 extension.

How does retatrutide work?

Retatrutide works by simultaneously activating three metabolic receptors: GLP-1 (slows digestion and suppresses appetite), GIP (improves insulin response), and glucagon (raises resting energy expenditure by roughly 6%). The triple-agonist design attacks weight loss from both intake (appetite suppression) and expenditure (energy burn), which produces deeper weight loss than dual-agonists like tirzepatide.

How is retatrutide typically administered?

Retatrutide is administered as a once-weekly subcutaneous injection in clinical trials. Final dosing protocols are being determined by ongoing Phase 3 programs. The compound is not commercially available for prescription as of May 2026.

What are the side effects of retatrutide?

Reported side effects in clinical trials are primarily gastrointestinal, nausea, vomiting, diarrhea, decreased appetite, consistent with the GLP-1 drug class. The glucagon component adds concerns about heart rate elevation and potential liver enzyme changes, both under ongoing evaluation in Phase 3.

Is retatrutide FDA approved?

No. Retatrutide is investigational and in Phase 3 clinical trials. FDA approval would depend on the full phase 3 package and a submitted NDA. Lilly has not announced a final approval date.

When will retatrutide be FDA approved?

As of May 2026 there is no announced FDA approval date. Eli Lilly's pivotal phase 3 obesity trial (TRIUMPH-1) read out in May 2026 with 28.3% weight loss at 80 weeks. TRIUMPH-2 (type 2 diabetes) and TRIUMPH-3 (cardiovascular disease) are expected to read out later in 2026. NDA filing depends on the full phase 3 package; analyst estimates point to Q4 2026, not Lilly-confirmed.

How much does retatrutide cost?

Retatrutide is not yet commercially available; no clinical retail price exists. On the research-chemical market it tends to price higher than simpler peptides, reflecting the synthesis complexity of the triple-agonist molecule.

related peptides

• tirzepatide — dual-agonist predecessor
• semaglutide — first-gen GLP-1 benchmark
• liraglutide — original in the class

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.