Retatrutide Dosage: What the Trials Actually Used

Updated July 29, 2026 · Sources: NEJM Phase 2 data, ClinicalTrials.gov TRIUMPH program

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, and the published schedule doubled the dose at each step rather than moving through intermediate values. The trial 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

Worth being precise here, because intermediate steps like 6 mg circulate widely in community protocols: no 6 mg dose was used in the published trials. The escalation was 2 → 4 → 8 → 12 mg. An intermediate step is not a trial-derived protocol, whatever its practical merits for tolerability.

Nausea, vomiting and diarrhea were the most common adverse events in the trials, and they clustered around dose increases rather than appearing at random. Holding a dose level longer before stepping up was the mitigation used in protocol design.

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%
TRIUMPH-1	104 weeks	−30.3%
TRIUMPH-3	80 weeks	−22.6%

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.

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.

Peptide preset

Peptide in vial (mg)

Bacteriostatic water added (ml)

Desired dose (mcg)

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Concentration (mcg / ml)

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Volume to draw (ml)

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Units on U-100 insulin syringe

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Doses per vial

Draw to this mark on a 1 ml U-100 insulin syringe

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 dose	4 mg dose	8 mg dose
10 mg	1 ml	10 mg/ml	20 units	40 units	80 units
10 mg	2 ml	5 mg/ml	40 units	80 units	—
20 mg	2 ml	10 mg/ml	20 units	40 units	80 units

At 8 mg weekly a 10 mg vial lasts a little over one week, so higher-dose protocols consume material quickly. That is the main driver of monthly cost, 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.

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Frequently asked questions

What retatrutide doses were used in clinical trials?

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, with gradual escalation from a low starting dose. The 8 mg and 12 mg arms produced the largest weight reductions at 48 weeks.

How is retatrutide titrated?

Most trial arms began at 2 mg weekly and stepped up every four weeks toward the target dose, though the 1 mg arm stayed at 1 mg throughout and one 4 mg arm started directly at 4 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, or slightly more than one 8 mg dose. At the higher trial doses a single 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

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

Related guides

Research use only. Retatrutide is an investigational compound not approved for human use. This page summarizes published trial data for informational purposes and is not medical advice.