Retatrutide Dosage: The Phase 2 Trial Escalation Explained

By DoseGauge Editorial · Updated 2026-06-12 · 5 min read

Retatrutide has no FDA-approved dose. It is an investigational triple GIP, GLP-1, and glucagon receptor agonist (Eli Lilly code LY3437943), not approved for any use as of June 2026, with Phase 3 trials (the TRIUMPH programme) ongoing. The dosing you will see online comes from clinical trials, not a prescribing label. In the NEJM Phase 2 obesity trial, the 12 mg arm escalated once weekly from 2 mg up to 12 mg over 12 weeks. The chart below reproduces that trial schedule. It is not a recommendation, and the calculator on this site only converts whatever dose you enter into the units to draw on a syringe.

The Phase 2 trial escalation

In the Phase 2 obesity trial (Jastreboff et al., NEJM 2023), participants assigned to the highest target dose started at 2 mg once weekly and stepped up every 4 weeks until they reached 12 mg. The table reproduces that escalation. Read it as a record of what the trial did, not as a schedule anyone should follow on their own.

The trial tested several target doses, not just 12 mg. Participants were randomized across 1 mg, 4 mg, 8 mg, and 12 mg target groups (some with different starting steps), plus placebo. The 12 mg target shown above was the highest studied. The escalation matters because the starting dose and the maintenance dose are different numbers: the early weeks at 2 mg and 4 mg were a ramp, not the dose the arm was built around.

Retatrutide has a half-life of about 6 days, which is what allowed once-weekly injection in the trial. Steady state builds over roughly 4 to 5 weeks of weekly dosing, so the 4-week spacing between steps also gave each dose time to reach a stable level before the next increase.

Why the dose escalates

The step-up pattern is about tolerability. In the trial, the most common adverse events were gastrointestinal (nausea, diarrhea, vomiting, constipation), they were dose-related, and they were mostly mild to moderate. Starting low and increasing slowly is the standard way incretin-based drugs are introduced in trials to limit those early gastrointestinal effects.

A slower ramp does not change the target dose, only the path to it. The trial spaced increases 4 weeks apart so each dose had time to settle before the next step. None of this is advice on how fast to move. It is a description of how the published trial was run, and the pace of any real escalation is a clinical decision, not something a chart can set.

Converting a dose to syringe units

A dose in milligrams does not tell you how far to pull the plunger. That depends on how you reconstituted the vial, because the volume of bacteriostatic water you add sets the concentration:

concentration (mg/mL) = vial strength (mg) / water added (mL)
draw volume (mL)       = dose (mg) / concentration (mg/mL)
units (U-100 syringe)  = draw volume (mL) x 100

Worked example. Put 1 mL of bacteriostatic water into a 10 mg vial and the concentration is 10 mg/mL. A 2 mg dose is then 2 / 10 = 0.20 mL, which is 20 units on a U-100 insulin syringe, and that 10 mg vial holds 5 such 2 mg amounts. Change the water volume and every number changes: the same 10 mg vial in 2 mL is 5 mg/mL, so 2 mg becomes 0.40 mL, or 40 units.

Because the units depend on your specific vial and water amounts, the reliable way to get the number is to compute it from your own inputs rather than copy a figure from a forum. The calculator does that conversion and flags the draw volume so you can see whether a dose fits a single U-100 syringe.

Frequently asked questions

Is there an approved retatrutide dose?

No. Retatrutide is investigational and not approved by the FDA for any indication as of June 2026, so there is no labeled or recommended dose. Every dose figure in circulation, including the escalation above, comes from clinical trials. Any use sits under a clinical trial or investigational protocol, and a clinician makes those decisions.

What was the highest dose studied in the Phase 2 trial?

The highest target dose in the NEJM Phase 2 obesity trial was 12 mg once weekly, reached by escalating from 2 mg in steps every 4 weeks. The trial also studied 1 mg, 4 mg, and 8 mg target doses against placebo. These are trial doses, not a recommendation.

How often was retatrutide injected in the trial?

Once weekly, subcutaneously. Its half-life of roughly 6 days supports weekly dosing, and steady state is reached over about 4 to 5 weeks of weekly injections.

How many units is a 2 mg retatrutide dose?

It depends on your concentration. At 10 mg/mL (a 10 mg vial in 1 mL of bacteriostatic water), 2 mg is 0.20 mL, or 20 units on a U-100 syringe. At 5 mg/mL it is 0.40 mL, or 40 units. Enter your own vial size and water volume in the calculator above for your exact number.

Informational and educational only. Not medical advice. DoseGauge computes from the values you enter and does not recommend a dose. Talk to a licensed clinician before using any peptide or GLP-1 medication.