Doses in the phase 2 trial
Retatrutide (LY3437943, Eli Lilly) acts on the GIP, GLP-1 and glucagon receptors. Its phase 2 trial gave it under the skin once a week for 48 weeks to 338 adults with obesity, or overweight with a weight-related condition, in six arms from 1 to 12 mg. Most arms started lower and stepped up to their dose.
| Arm, once a week | Doses | Weight at 48 weeks |
|---|---|---|
| 1 mg | 1 mg each week | −8.7% |
| 4 mg, start 2 mg | 2 mg, then 4 mg | −17.1%both 4 mg arms |
| 4 mg, start 4 mg | 4 mg each week | |
| 8 mg, start 2 mg | 2 mg, then 4 mg, then 8 mg | −22.8%both 8 mg arms |
| 8 mg, start 4 mg | 4 mg, then 8 mg | |
| 12 mg, start 2 mg | 2 mg, then 4, 8 and 12 mg | −24.2% |
The most common side effects were gastrointestinal. They rose with the dose and were partly lessened by starting at 2 mg rather than 4 mg. The registry and the paper’s abstract give the steps of each arm, not the weeks spent on each step.
Each trial dose in units
The same dose is a different number of units at each strength. The table shows the units on a U-100 syringe at three strengths; the calculator above works out any other.
| Dose | at 5 mg/mL | at 10 mg/mL | at 20 mg/mL |
|---|---|---|---|
| 1 mg | 20 | 10 | 5 |
| 2 mg | 40 | 20 | 10 |
| 4 mg | 80 | 40 | 20 |
| 8 mg | over 100 | 80 | 40 |
| 12 mg | over 100 | over 100 | 60 |
The strength is the mg in the vial divided by the mL of water added: 10 mg with 2 mL is 5 mg per mL, 10 mg with 1 mL is 10 mg per mL. The water for a 10 mg vial and a 30 mg vial, with each trial dose in units, is on their own pages.
The example in the calculator. 10 mg with 2 mL of water is 5 mg per mL. The trial’s 2 mg starting dose is 2 ÷ 5 = 0.4 mL, which is 40 units on a U-100 syringe, and the vial holds 5 such doses.
Is retatrutide FDA-approved?
No. Retatrutide is an investigational drug in phase 3 trials, and the FDA has not approved it for any use.
- FDA
- Not approved, and cannot be used in compounding under federal law. It is not a component of any FDA-approved drug and has not been found safe and effective for any condition. FDA has warned telehealth companies, ingredient distributors and outsourcing facilities over retatrutide, and companies selling it labelled “for research purposes” or “not for human consumption”.
- Advisory committee
- Not on the agenda of the Pharmacy Compounding Advisory Committee (meetings of October and December 2024 and July 2026), and not among the substances nominated for compounding under section 503A (FDA list updated 2026-05-14).
- WADA
- Not named on the 2026 Prohibited List or on the 2027 List. Its section S0 prohibits at all times any substance the List does not cover elsewhere that has no approval for human therapeutic use, such as drugs in clinical development.
- Trials
- Phase 3 (TRIUMPH): TRIUMPH-1 to TRIUMPH-4 completed, TRIUMPH-5 to TRIUMPH-9 active, not recruiting; no results posted on ClinicalTrials.gov.
- DailyMed
- Its retatrutide listings carry the marketing category “Export only”: a seller’s listing, not an FDA approval.
Other calculators
- How much bacteriostatic water for 10 mg retatrutideThe water to add to a 10 mg retatrutide vial so your dose is the number of units you want to draw.
- How much bacteriostatic water for 30 mg retatrutideThe water to add to a 30 mg retatrutide vial so your dose is the number of units you want to draw.
- Tirzepatide dosage calculatorUnits to draw for a tirzepatide dose, from the mg in the vial and the mL of liquid in it.
- GLP-1 dosage chartsStart, step-up, maintenance and maximum doses of each GLP-1 medicine as its FDA label gives them, with the label's date.
- Semaglutide units to mgThe mg in the units you draw of a semaglutide vial, or the units for a dose, from the strength printed on the vial.
Questions
How many units is 2 mg of retatrutide?
It depends on the strength of the vial. At 5 mg per mL it is 40 units, at 10 mg per mL 20 units, at 20 mg per mL 10 units.
What doses did the retatrutide trials use?
The phase 2 trial used 1, 4, 8 and 12 mg once a week. Four arms started lower and stepped up: to 4 mg and to 8 mg from 2 mg, to 8 mg from 4 mg, and to 12 mg from 2 mg. The 1 mg arm and one 4 mg arm took their dose from the start. The phase 3 registry entries give no doses in mg: they name them Dose 1, Dose 2 and so on.
How much weight did people lose in the trial?
At 48 weeks the mean change in body weight was −8.7% with 1 mg, −17.1% with 4 mg, −22.8% with 8 mg and −24.2% with 12 mg, against −2.1% with placebo.
Is retatrutide FDA-approved?
No. As of 2026-10-01 the FDA says it is not a component of any FDA-approved drug and cannot be used in compounding under federal law.
Sources
- Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trialN Engl J Med 2023;389:514–526, PubMed 37366315. Abstract: the six dose arms, the 48-week weight change, side effects and the starting dose.
- NCT04881760: phase 2 study of LY3437943 in obesity or overweightClinicalTrials.gov, record retrieved 2026-10-28. Arms and interventions: the steps of each arm; completed.
- FDA’s concerns with unapproved GLP-1 drugs used for weight lossFDA, content current as of 2026-10-01. Retatrutide cannot be used in compounding; warnings to sellers.
- Bulk drug substances nominated for use in compounding under section 503AFDA, list updated 2026-05-14. Retatrutide is not on it.
- WADA Prohibited List 2026In effect 2026-01-01. S0, non-approved substances.
- BD Insulin Syringe, 510(k) K190054FDA, cleared 2019-10-21. U-100 syringes of 0.3, 0.5 and 1 mL and their lines.