Retatrutide Dosage: What the Trials Actually Used
Retatrutide is a triple agonist — it activates the GIP, GLP-1 and glucagon receptors at once, which is one more target than tirzepatide and two more than semaglutide. That extra glucagon activity is also why the dose escalation matters more here than with earlier compounds: the published protocols never start at a therapeutic dose.
Doses used in the Phase 2 obesity trial
The 48-week Phase 2 trial randomized 338 adults with obesity across six retatrutide arms and placebo, all administered once weekly by subcutaneous injection. Six arms but four dose levels — because two of the levels were tested with two different starting doses:
| Weekly dose | Escalation used | Reported mean weight change at 48 weeks |
|---|---|---|
| 1 mg | No escalation — 1 mg throughout | −8.7% |
| 4 mg | 2 mg start, or 4 mg from the outset | ≈ −17% |
| 8 mg | 2 mg start or 4 mg start | −22.8% |
| 12 mg | 2 mg start only | −24.2% |
Two things stand out. First, the dose–response curve is steep from 1 mg to 8 mg and then flattens: the 12 mg arm added little over 8 mg while producing more gastrointestinal complaints. Second, weight was still declining when the trial ended, meaning 48 weeks did not reach a plateau.
The titration principle
Arms that escalated did so in four-week steps. Phase 2 doubled the dose at each step rather than moving through intermediate values — the escalation toward 8 mg was:
| Weeks | Weekly dose | Purpose |
|---|---|---|
| 1–4 | 2 mg | Establish tolerability |
| 5–8 | 4 mg | First step up |
| 9+ | 8 mg | Target maintenance dose |
Phase 3 changed this, and the change is the source of a lot of confusion about the 6 mg dose that circulates in community protocols. The TRIUMPH trials start every participant at 2 mg and step up every four weeks to a target of 4 mg, 9 mg or 12 mg — and the routes to the two higher targets both pass through 6 mg:
| Target dose | Steps used to reach it |
|---|---|
| 4 mg | 2 mg → 4 mg |
| 9 mg | 2 mg → 4 mg → 6 mg → 9 mg |
| 12 mg | 2 mg → 4 mg → 6 mg → 9 mg → 12 mg |
So the precise statement is this: 6 mg was used in Phase 3, but only as a four-week titration step, never as a maintenance dose. No trial has tested what happens if you stop at 6 mg and stay there — the target doses studied are 4, 9 and 12 mg. That distinction matters, because people sitting at 6 mg indefinitely often describe it as a trial dose, and it is not one.
One caveat on the source. These step values come from Eli Lilly's press releases, which state them explicitly. The ClinicalTrials.gov records label the arms only as "Dose 1 / Dose 2 / Dose 3" and the published trial-design paper says only "a fixed dose escalation regimen," so there is currently no peer-reviewed publication of the schedule.
What Phase 3 has reported
Phase 2 is no longer the newest data. The Phase 3 TRIUMPH program has begun reporting, and the results run higher than Phase 2 did — largely because the trials ran longer and weight was still declining when Phase 2 ended at 48 weeks.
| Trial | Duration | Reported mean weight reduction |
|---|---|---|
| Phase 2 (obesity) | 48 weeks | −24.2% at 12 mg |
| TRIUMPH-1 | 80 weeks | −28.3% efficacy / −25.0% treatment-regimen |
| TRIUMPH-1 extension | 104 weeks | −30.3% — selected subgroup, n=532 |
| TRIUMPH-2 (type 2 diabetes) | 80 weeks | −20.8% efficacy |
| TRIUMPH-3 (obesity + cardiovascular disease) | 80 weeks | −22.6% efficacy |
The pattern across both phases is the same: the curve keeps descending well past the point where earlier incretin trials flattened. Dosing in Phase 3 follows the same titrate-slowly principle established in Phase 2, with the addition of the 6 mg step.
Read the 104-week figure carefully. That extension included only participants with a BMI of 35 or above who finished the first 80 weeks and tolerated their dose, and it escalated them to their maximum tolerated dose — so it is a selected subgroup, not the whole trial carried further. None of the TRIUMPH results has been peer-reviewed yet.
Reconstitution math for a 10 mg vial
Retatrutide ships as a lyophilized powder, so the weekly dose has to be converted into a syringe volume. Enter your vial size and water volume below.
Formula: concentration = peptide (mcg) ÷ water (ml). Volume = dose ÷ concentration. One unit on a U-100 insulin syringe = 0.01 ml. Values are for laboratory reference only.
| Vial | Water | Concentration | 2 mg | 4 mg | 6 mg | 9 mg |
|---|---|---|---|---|---|---|
| 10 mg | 1 ml | 10 mg/ml | 20 units | 40 units | 60 units | 90 units |
| 10 mg | 2 ml | 5 mg/ml | 40 units | 80 units | — | — |
| 20 mg | 2 ml | 10 mg/ml | 20 units | 40 units | 60 units | 90 units |
The dashes are not rounding. A standard U-100 insulin syringe holds 100 units, so at 5 mg/ml a 6 mg dose would need 120 units — more than the syringe holds. Diluting a vial too far quietly puts the higher doses out of reach in a single injection, which is the most common reconstitution mistake at these dose levels.
At 9 mg weekly a 10 mg vial covers a single dose, so the Phase 3 target doses consume material quickly. That is the main driver of monthly cost, far more than the per-vial price.
How retatrutide dosing compares
| Compound | Receptor targets | Typical trial range |
|---|---|---|
| Semaglutide | GLP-1 | 0.25 → 2.4 mg weekly |
| Tirzepatide | GIP + GLP-1 | 2.5 → 15 mg weekly |
| Retatrutide | GIP + GLP-1 + glucagon | 1 → 12 mg weekly |
Milligram figures are not comparable across molecules — each has its own potency at its own receptors. A 2 mg retatrutide dose is not equivalent to 2 mg of tirzepatide.
Retatrutide (RTA) — American Peptides
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Frequently asked questions
What retatrutide doses were used in clinical trials?
Phase 2 and Phase 3 used different dose sets. The Phase 2 obesity trial published in the New England Journal of Medicine tested 1 mg, 4 mg, 8 mg and 12 mg once weekly. The Phase 3 TRIUMPH trials dropped the 8 mg target and use 4 mg, 9 mg and 12 mg instead, reached by stepping through 2 mg and — for the two higher targets — 6 mg.
Was 6 mg of retatrutide used in trials?
Yes, but only as a titration step, and this distinction is the one most often lost. In Phase 3 every participant targeting 9 mg or 12 mg passes through 6 mg for four weeks on the way up. No trial has tested 6 mg as a maintenance dose, so there is no trial evidence for what happens if you stop there and stay. The target doses actually studied are 4, 9 and 12 mg.
How is retatrutide titrated?
In Phase 3 every participant starts at 2 mg weekly and steps up every four weeks: 2 to 4 mg for the 4 mg target, 2 to 4 to 6 to 9 mg for the 9 mg target, and 2 to 4 to 6 to 9 to 12 mg for the 12 mg target. Phase 2 escalated differently, doubling from 2 to 4 to 8 to 12 mg. Escalating slowly is what makes the gastrointestinal side effects manageable; jumping straight to a high dose is where most tolerability problems come from.
How does retatrutide dosing compare with tirzepatide?
The milligram numbers look similar — both are titrated in the 2 mg to 12–15 mg weekly range — but they are not interchangeable. Retatrutide is a triple GIP/GLP-1/glucagon agonist, so the glucagon component adds an effect tirzepatide does not have.
How many doses are in a 10 mg vial of retatrutide?
A 10 mg vial provides five 2 mg doses, two and a half 4 mg doses, or a single 9 mg dose with a little left over. At the Phase 3 target doses one vial covers roughly one week, which is why cost per month rises sharply with dose.
Is retatrutide approved by the FDA?
No. As of mid-2026 retatrutide remains an investigational compound in Phase 3 trials and is not approved for human use. Material sold online is designated for laboratory research only.
Sources
- Eli Lilly. TRIUMPH-1 topline results, 21 May 2026. Company announcement. Not peer-reviewed; presented at ADA, June 2026.
- Eli Lilly. TRIUMPH-1 sub-study results in obstructive sleep apnoea and knee osteoarthritis, 6 June 2026. Company announcement. Not peer-reviewed.
- Eli Lilly. TRIUMPH-2 and TRIUMPH-3 topline results and the stated Q1 2027 BLA submission plan, 23 July 2026. Company announcement. Not peer-reviewed.
- Phase 3 registry records: TRIUMPH-1 (NCT05929066), TRIUMPH-2 (NCT05929079), TRIUMPH-3 (NCT05882045), TRIUMPH-4 (NCT05931367).
- Giblin K et al. Retatrutide for the treatment of obesity, obstructive sleep apnoea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism, 2026;28(1):83–93. PubMed
- Jastreboff AM et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 2023;389(6):514–526. PubMed
- Rosenstock J et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. The Lancet, 2023;402(10401):529–544. PubMed
- Eli Lilly TRIUMPH Phase 3 program: TRIUMPH-1 (NCT05929066), TRIUMPH-2 (NCT05929079), TRIUMPH-3 (NCT05882045). Design and titration protocols: Giblin K et al. Diabetes, Obesity and Metabolism, 2026;28(1):83–93. PubMed
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