Retatrutide is Eli Lilly's investigational triple agonist (GLP-1 / GIP / glucagon). As of May 2026 it is not FDA-approved — it's still in Phase 3 trials. This page summarizes what the published trial data show about how retatrutide has been dosed in clinical studies, and what an approved label might plausibly look like if approval comes through.
Important: This page is informational only and is not medical advice. Decisions about whether and how to use any medication belong with you and a licensed clinician.
Retatrutide activates GLP-1 receptors (like semaglutide), GIP receptors (like tirzepatide), and glucagon receptors. The glucagon component is the new piece, and it's the most likely explanation for the differences from tirzepatide seen in the trial data — both the higher reported weight loss and a few side effects that haven't been seen at this rate with tirzepatide.
What the published data show:
The 9 mg dose is notable. In TRIUMPH-4 it produced nearly the same weight loss as 12 mg with materially less GI burden and a third lower discontinuation rate. If retatrutide is eventually approved, it's plausible that 9 mg emerges as a common maintenance dose rather than 12 mg.
Across the TRIUMPH Phase 3 program, participants started at 2 mg once weekly, with the dose escalated in 4-week intervals to a randomized target dose, then maintained for the remainder of the 68- or 80-week treatment period. TRIUMPH-4 specifically tested the 9 mg and 12 mg target doses (no 4 mg arm); other Phase 3 trials in the program also include 4 mg.
The published titration ladder for the program looks like this:
| Weeks | 4 mg target | 9 mg target | 12 mg target |
|---|---|---|---|
| 1–4 | 2 mg | 2 mg | 2 mg |
| 5–8 | 4 mg | 4 mg | 4 mg |
| 9–12 | 4 mg | 6 mg | 6 mg |
| 13–16 | 4 mg | 9 mg | 9 mg |
| 17+ | 4 mg | 9 mg | 12 mg |
A few facts about how the trials handled dosing:
If retatrutide is approved, the FDA-approved label could look similar to this ladder — but it could also differ in starting dose, escalation timing, available maintenance doses, or maximum dose. The trial protocol is not a label.
Both arms started at 2 mg, both used 4-week titration intervals, both ran 68 weeks. Baseline averages: ~248.5 lbs and BMI 40.4. All figures below are from Lilly Medical's preliminary results disclosure for TRIUMPH-4.
| Outcome (efficacy estimand) | 9 mg | 12 mg | Placebo |
|---|---|---|---|
| Weight loss, % | −26.4% | −28.7% | −2.1% |
| Weight loss, lbs | −64.2 lbs | −71.2 lbs | −4.6 lbs |
| Achieved ≥25% weight loss | 47.7% | 58.6% | 1.3% |
| Achieved ≥30% weight loss | 30.5% | 39.4% | 0.8% |
| Achieved ≥35% weight loss | 18.2% | 23.7% | 0.0% |
| WOMAC pain reduction (points / %) | −4.5 (−75.8%) | −4.4 (−74.3%) | −2.4 (−40.3%) |
| Pain-free at week 68 | 14.1% | 12.0% | 4.2% |
| Nausea | 38.1% | 43.2% | 10.7% |
| Vomiting | 20.4% | 20.9% | 0% |
| Diarrhea | 34.7% | 33.1% | 13.4% |
| Constipation | 21.8% | 25.0% | 8.7% |
| Dysesthesia | 8.8% | 20.9% | 0.7% |
| Discontinued due to adverse events | 12.2% | 18.2% | 4.0% |
The 12 mg arm produced more weight loss. The 9 mg arm produced essentially the same WOMAC pain reduction with about half the dysesthesia and a notably lower AE discontinuation rate.
A handful of compounding-pharmacy clinicians and online retatrutide communities have described a slower variant of the trial titration — extending each step from 4 weeks to 6 or 8 weeks, on the theory that retatrutide's higher GI burden and heart rate signal warrant a gentler ramp. No clinical trial has tested this approach.
A representative version of what people have described looks like this:
| Weeks | Dose | Time at Dose |
|---|---|---|
| 1–8 | 2 mg | 8 weeks |
| 9–16 | 4 mg | 8 weeks |
| 17–24 | 6 mg | 8 weeks |
| 25–32 | 9 mg | 8 weeks |
| 33+ | 12 mg | Ongoing |
Without trial data there's no way to know how this compares to the standard schedule on efficacy or safety.
Some users of compounded retatrutide describe starting at sub-trial doses — below 2 mg per week — and gradually working up. These schedules have no clinical trial support. No published trial has formally evaluated retatrutide doses below 2 mg as a sustained regimen.
A typical schedule reported in online communities looks something like this:
| Weeks | Dose |
|---|---|
| 1–2 | 0.25–0.5 mg |
| 3–4 | 0.5–1.0 mg |
| 5–8 | 1.0–1.5 mg |
| 9–12 | 1.5–2.0 mg |
| 13+ | 2 mg (then onto the trial-style ladder, if continued) |
There is no clinical evidence that microdosing retatrutide is safe, effective, or preferable to the trial protocol. People who report doing it most often cite a desire to minimize side effects or to start gently with an investigational drug.
Because retatrutide is not approved, any retatrutide currently available in the US comes from compounding pharmacies or research-peptide channels. The FDA does not regulate quality, potency, or sterility of these products. Compounding pharmacies are typically permitted to prepare versions of FDA-approved drugs that are in shortage — but retatrutide isn't an approved drug, so the shortage pathway doesn't apply, and the legal status of these products is more uncertain than for compounded tirzepatide or semaglutide.
The most common error in compounded GLP-1 use is arithmetic — drawing the wrong number of units because of a math mistake. The tables below are included so people who are using compounded retatrutide can at least get the dose math right.
Compounded retatrutide vials usually arrive lyophilized (powder) and are reconstituted with bacteriostatic water. The most common reconstitution gives 10 mg/mL (e.g., a 30 mg vial mixed with 3 mL of BAC water). The concentration determines how many syringe units correspond to a given milligram dose.
| Dose | Units to Draw |
|---|---|
| 0.5 mg | 10 units |
| 1.0 mg | 20 units |
| 2.0 mg | 40 units |
| 4.0 mg | 80 units |
| 6.0 mg | 120 units* |
| 9.0 mg | 180 units* |
| 12 mg | 240 units* |
*Exceeds a standard U-100 insulin syringe; would require a larger syringe or multiple injections
| Dose | Units to Draw |
|---|---|
| 0.5 mg | 5 units |
| 1.0 mg | 10 units |
| 2.0 mg | 20 units |
| 4.0 mg | 40 units |
| 6.0 mg | 60 units |
| 9.0 mg | 90 units |
| 12 mg | 120 units* |
*Exceeds a standard U-100 insulin syringe
| Dose | Units to Draw |
|---|---|
| 1.0 mg | 7 units |
| 2.0 mg | 13 units |
| 4.0 mg | 27 units |
| 6.0 mg | 40 units |
| 9.0 mg | 60 units |
| 12 mg | 80 units |
Values are rounded to whole syringe units (the smallest practical increment).
If you're trying to figure out the concentration of a vial you already have, our finding your medication concentration guide and our Reconstitution Calculator may help. The Retatrutide Dose Calculator handles the mg-to-units arithmetic.
| Tirzepatide (approved) | Retatrutide (investigational) | |
|---|---|---|
| Mechanism | GLP-1 + GIP | GLP-1 + GIP + glucagon |
| FDA status | Approved (Mounjaro, Zepbound) | Investigational; Phase 3 |
| Trial starting dose | 2.5 mg weekly | 2 mg weekly |
| Trial titration cadence | Every 4 weeks | Every 4 weeks |
| Trial dose ladder | 2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg | 2 → 4 → 6 → 9 → 12 mg |
| Highest dose tested in pivotal trials | 15 mg | 12 mg |
| Weeks to top dose in trial | 20 | 16 |
| Average weight loss in pivotal trials | ~22.5% at 72 weeks (SURMOUNT-1, obesity-only) | ~28.7% at 68 weeks (TRIUMPH-4, obesity + knee OA)* |
| Distinctive adverse events | GI | GI (higher rates); ~6 bpm heart rate rise; dysesthesia |
*The most direct head-to-head obesity comparator for retatrutide will be TRIUMPH-1 (Phase 3, obesity-only, 80 weeks), which had not read out as of this writing. TRIUMPH-4 enrolled participants with obesity and knee osteoarthritis.
Here's what the published TRIUMPH protocols actually permitted:
Some compounded retatrutide users describe splitting their weekly dose into two or three smaller injections through the week. The community rationale is that flatter peak drug levels may reduce nausea and the heart rate signal — same total weekly amount, lower Cmax. There is no published clinical data on split dosing of retatrutide.
If someone is exploring this with their clinician, our Split Dose Calculator can do the arithmetic of converting a weekly dose into a custom schedule.
On Lilly's Q4 2025 earnings call, the company guided to filing FDA applications for retatrutide in obesity, obstructive sleep apnea, and knee osteoarthritis at some point during 2026, pending the remaining TRIUMPH Phase 3 readouts (TRIUMPH-1, the pivotal obesity readout, was expected later in Q2 2026 per the Q1 2026 earnings call). With a standard FDA review window — and priority review plausible given the combined obesity / OA pain data — an approval decision in 2027 is on the table. Until then:
If retatrutide is approved, this page will be updated to reflect the actual label.
This page was last updated in May 2026. TRIUMPH-4 efficacy and safety figures are from Lilly Medical's preliminary results disclosure (Lilly USA, 2026). Phase 3 protocol details are from the published TRIUMPH design paper (Giblin K et al., Diabetes, Obesity and Metabolism, published online October 2025; 2026;28(1):83–93). Phase 2 data are from Jastreboff AM et al., New England Journal of Medicine 2023;389(6):514–526. Regulatory timing is from Lilly's Q4 2025 (Feb 4, 2026) and Q1 2026 (Apr 30, 2026) earnings calls. Retatrutide is investigational and has no FDA-approved label.