Retatrutide Titration Schedule Explained

Last updated: June 2026

Retatrutide is an investigational, once-weekly injectable that the phase-2 trials escalated slowly — starting at 2–4 mg and stepping up roughly every four weeks toward a maintenance dose of 4, 8, or 12 mg. It is not FDA-approved and has no official patient dosing schedule; the numbers below are the escalation used in published clinical trials, shown so you can understand the pattern and convert any milligram dose to syringe units — not a protocol to follow.

Have a vial and a target milligram dose? Convert it to exact mL and U-100 syringe units instantly.

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TL;DR — key takeaways

Investigational. Retatrutide (LY3437943) is a triple GIP + GLP-1 + glucagon receptor agonist still in clinical development. There is no approved label and no approved titration schedule.
Slow build. The phase-2 obesity trial used initial doses of 2 mg or 4 mg once weekly and increased gradually, about every four weeks, to a target maintenance dose of 4, 8, or 12 mg over 48 weeks.
Why step up at all. Like other incretin drugs, the appetite and gut effects that drive weight loss also cause early nausea, so trials start low to improve tolerability.
Units follow concentration. How many syringe units you draw depends on your vial's mg/mL strength, not on the drug name — the same arithmetic used for any reconstituted peptide.

What retatrutide is (and isn't yet)

Retatrutide is a single molecule that activates three receptors at once: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor. The GLP-1 and GIP arms behave like the incretin effects seen with semaglutide and tirzepatide; the added glucagon-receptor activity is thought to raise energy expenditure, which is the feature that distinguishes retatrutide from those two drugs.

It is important to be blunt about status: as of this writing retatrutide has completed phase-2 trials and is in phase-3 testing. It is not approved by the FDA or any major regulator, so there is no prescribing information, no approved starting dose, and no official titration schedule. Everything described here comes from peer-reviewed trial reports and is educational only.

The phase-2 escalation, by the numbers

In the 48-week phase-2 obesity trial, participants received retatrutide once weekly by subcutaneous injection. Rather than starting everyone at their target dose, the trial assigned a low initial dose and stepped it up gradually, roughly every four weeks, until the assigned maintenance dose was reached. The documented dose arms are below.

Trial arm (maintenance)	Initial dose	Frequency	Direction
1 mg	1 mg	Once weekly	Little/no escalation
4 mg	2 mg or 4 mg	Once weekly	Step up ~every 4 weeks
8 mg	2 mg or 4 mg	Once weekly	Step up ~every 4 weeks
12 mg	2 mg	Once weekly	Step up ~every 4 weeks

At the highest dose (12 mg) the trial reported mean weight reduction of roughly 24% at 48 weeks, with the lower arms producing proportionally less. A separate phase-2 trial in type-2 diabetes used a similar weekly, gradually escalated design. The four-week cadence mirrors approved incretins — for context, the tirzepatide (Zepbound) label also holds each dose for at least four weeks before any increase.

The escalation staircase, visualised

The chart below is an illustrative once-weekly climb toward the 12 mg arm — the exact intermediate steps were set by the trial protocol, but the shape is the familiar incretin staircase: hold each rung about four weeks, then step up.

Turning a milligram dose into syringe units

Retatrutide ships as a freeze-dried powder you reconstitute with bacteriostatic (BAC) water, so the milligram dose on the trial chart is never what you read on the syringe — you read units. A U-100 insulin syringe has 100 units per 1 mL. The conversion is always the same: find the concentration (mg/mL), divide your dose by it to get mL, then multiply by 100 to get units.

Worked example 1 — set the concentration

You have a 10 mg vial and add 2 mL of BAC water.

10 mg ÷ 2 mL = 5 mg/mL. That single number drives every draw below.

Worked example 2 — the 2 mg starting dose

Target 2 mg from a 5 mg/mL vial.

2 mg ÷ 5 mg/mL = 0.4 mL. 0.4 mL × 100 units/mL = 40 units.

Draw 40 units on a U-100 syringe.

Worked example 3 — the 4 mg step

Target 4 mg from a 10 mg/mL vial (10 mg vial + 1 mL BAC).

4 mg ÷ 10 mg/mL = 0.4 mL. 0.4 mL × 100 = 40 units.

Same 40 units as the 2 mg dose above — because this vial is twice as strong.

Worked example 4 — the 8 mg step

Target 8 mg from a 10 mg/mL vial.

8 mg ÷ 10 mg/mL = 0.8 mL. 0.8 mL × 100 = 80 units.

Draw 80 units — most of a 1 mL syringe.

Worked example 5 — the 12 mg top dose

Target 12 mg. At 10 mg/mL that needs 1.2 mL — more than a 1 mL syringe holds. Use a stronger 20 mg/mL vial instead.

12 mg ÷ 20 mg/mL = 0.6 mL. 0.6 mL × 100 = 60 units.

Worked example 6 — doses per vial

A 10 mg vial dosed at the 2 mg starting amount holds 10 ÷ 2 = 5 weekly doses, after which the early weeks of an escalation would need a fresh vial.

Dose-to-units reference chart

Each trial dose shown as units on a U-100 syringe at two common reconstituted strengths. Always confirm against your own vial label.

Weekly dose	At 5 mg/mL	At 10 mg/mL
2 mg (start)	40 units	20 units
4 mg	80 units	40 units
8 mg	— (over 1 mL)	80 units
12 mg	— (over 1 mL)	— (over 1 mL)

The blanks are the point: at 5 mg/mL, an 8 mg dose needs 1.6 mL and a 12 mg dose needs 2.4 mL, both larger than a standard 1 mL syringe. Higher doses force a higher-concentration vial — which is exactly the trade-off the calculator makes visible.

How this is calculated

Every unit figure here rests on two facts only: a U-100 syringe holds 100 units per mL, and concentration is dose divided by volume. There is no retatrutide-specific constant — the same arithmetic applies to semaglutide, tirzepatide, or any vialled peptide. The dose schedule itself is reported from clinical trials, rounded for clarity; it is not a recommendation. This page is an education and maths tool, not medical advice, and the dose numbers are investigational. Any actual use of retatrutide should follow a qualified prescriber, who sets the starting dose and escalation.

Frequently asked questions

Is retatrutide FDA-approved?

No. As of this writing retatrutide has finished phase-2 trials and is in phase-3 development. It has no approved label, so there is no official patient dosing schedule. The doses here are taken from published trials for educational context only.

How is retatrutide different from tirzepatide?

Tirzepatide is a dual GIP/GLP-1 agonist; retatrutide adds a third action at the glucagon receptor, making it a triple agonist. That extra glucagon activity is thought to increase energy expenditure on top of the appetite and gut effects shared with other incretins.

Why start at 2 mg instead of the target dose?

The same gut-slowing and appetite effects that drive weight loss also cause early nausea. Starting low and stepping up about every four weeks lets the body adjust, which improves tolerability — the same reason semaglutide and tirzepatide titrate.

How many syringe units is a retatrutide dose?

It depends entirely on your vial's concentration, not the dose name. A 4 mg dose is 80 units from a 5 mg/mL vial but only 40 units from a 10 mg/mL vial. Work out mg/mL first, then divide and multiply by 100.

Sources

This guide is for general educational purposes only and does not constitute medical advice. Always follow your prescriber’s specific instructions and consult a qualified clinician before changing any protocol.