What is Retatrutide?
Retatrutide is an investigational once-weekly injection from Eli Lilly that activates three receptors at once: GIP, GLP-1, and glucagon. Tirzepatide hits the first two; retatrutide adds the third.
It has produced the largest weight loss numbers ever recorded in an obesity drug trial. In the phase 3 TRIUMPH-1 results reported in May 2026, participants on the top dose averaged 25.0% weight loss at 80 weeks and 30.3% — about 85 lbs — in the 104-week extension, with no plateau in the curve.
It is not approved and cannot be prescribed. On July 23, 2026 Lilly said it plans to file for approval in the first quarter of 2027, pushing back earlier guidance of a 2026 submission. With a standard review that puts a first decision in late 2027 or 2028.
Anything sold today as "retatrutide" — research vials, peptide sites, grey-market sellers — is unapproved and unregulated. No licensed US provider can legally prescribe or dispense it.
How it works
The GLP-1 and GIP arms work the way they do in tirzepatide: appetite drops, the stomach empties more slowly, and insulin response improves. The third arm is what is new.
Glucagon receptor agonism raises energy expenditure and pushes the liver to mobilise stored fat. Historically that was seen as a liability in diabetes drugs, since glucagon raises blood sugar — the bet in retatrutide is that pairing it with two incretin agonists cancels the glucose downside while keeping the metabolic-rate upside. The trial results so far suggest the bet is working.
Dosing schedule
There is no approved dosing schedule — the FDA has not reviewed the drug. These are the weekly doses studied in the phase 3 TRIUMPH program, shown for context only:
| Dose | When |
|---|---|
| 1 mg / week | Titration starting dose in trials |
| 4 mg / week | Lowest maintenance dose studied — 17.6% at 80 weeks |
| 9 mg / week | Mid dose — 23.7% at 80 weeks |
| 12 mg / week | Top dose studied — 25.0% at 80 weeks, 30.3% at 104 weeks |
Results in clinical trials
TRIUMPH-1, reported in May 2026, found average weight loss of 17.6% at 4 mg, 23.7% at 9 mg, and 25.0% at 12 mg over 80 weeks, versus 3.9% on placebo. In the pre-specified 104-week extension the 12 mg group reached 30.3% — roughly 85 lbs — with the weight curve still falling. At 80 weeks, 45.3% of participants on 12 mg had lost 30% or more of their body weight, a threshold previously associated with bariatric surgery. TRIUMPH-4, in adults with obesity and knee osteoarthritis, showed 28.7% weight loss at 68 weeks alongside significant pain relief.
Side effects
Common
- Nausea
- Diarrhea
- Vomiting
- Constipation
- Decreased appetite
- Increased heart rate
Serious (rare)
- Pancreatitis (class risk)
- Gallbladder disease (class risk)
- Kidney injury from dehydration
- Effects still under regulatory review
How much does Retatrutide cost?
There is no legitimate price, because there is no legal way to buy it. What follows is what is known about the eventual market:
| Route | Typical cost |
|---|---|
| Current US price | Not available — not approved |
| Expected earliest launch | 2028, if the Q1 2027 filing holds |
| Grey-market "research" vials | Illegal for human use — avoid entirely |
| Available alternative today | Zepbound (tirzepatide), ~20–22% average weight loss |
No US price exists until the FDA approves a drug. For what clinics charge for approved GLP-1s today, see our clinic pricing study.
Frequently asked questions
Is retatrutide FDA approved?
No. As of August 2026 it remains investigational. Lilly announced on July 23, 2026 that it plans to submit for approval in the first quarter of 2027, which puts a first FDA decision in late 2027 or early 2028 and a launch no earlier than 2028.
Can I get retatrutide from a clinic or telehealth provider?
No. No licensed US provider can prescribe it, and no pharmacy can legally dispense it, because it has no FDA approval. Any clinic offering it is operating outside the law, and any website selling vials is selling an unregulated product with no sterility, purity, or dosing guarantees.
How much better is retatrutide than Zepbound?
On trial averages, meaningfully: roughly 25% at 80 weeks and 30.3% at 104 weeks for retatrutide 12 mg, versus about 20–22.5% for tirzepatide. No head-to-head trial has been run, so cross-trial comparisons come with the usual caveats about different populations and protocols.
What should I do while waiting for retatrutide?
If you want treatment now, the approved options are the ones to discuss with a provider — Zepbound and Wegovy for weight management, or the newer oral options if injections are a barrier. Waiting two-plus years for an unapproved drug is rarely the right plan when approved ones are available.
Related medications
Guides
Primary sources
- Triple–hormone-receptor agonist retatrutide for obesity (phase 2) — New England Journal of Medicine
- Retatrutide achieves up to 30.3% average weight loss in phase 3 TRIUMPH-1 — AJMC
This page is for educational purposes only and is not medical advice. Retatrutide is an investigational drug that has not been approved by the FDA and cannot be legally prescribed or dispensed in the United States. Products sold online under this name are unregulated. GLPFinders is a directory service and does not prescribe, sell, or dispense medications.