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Retatrutide dosage: chart, trial doses and vial math
Retatrutide has been given once a week by injection under the skin. The Phase 3 obesity trial used 4 mg, 9 mg or 12 mg a week, and the earlier Phase 2 trial used 1 mg to 12 mg, starting at 2 mg or 4 mg. It is not an approved medicine, so there is no label dose.
Legal status
US Not approved, in trials
Canada Not authorized
Checked 10 Oct 2026What is Retatrutide?Retatrutide dosage chart
Trial doses, no labelPick your vial size. Each row shows the dose in milligrams or micrograms, the volume to draw and the mark on a U-100 syringe.
| Dose | Volume | Syringe units |
|---|---|---|
| 2 mg | 0.10 mL | 10 units |
| 4 mg | 0.20 mL | 20 units |
| 8 mg | 0.40 mL | 40 units |
| 9 mg | 0.45 mL | 45 units |
| 12 mg | 0.60 mL | 60 units |
Source Weekly doses given in the Phase 2 and Phase 3 obesity trials (NEJM 2023 and 2026). Vial math is arithmetic.
Which syringe fits each dose
For the 30 mg vial at 20 mg/mL.
| Dose | Volume | Units | 0.3 mL syringe | 0.5 mL syringe | 1 mL syringe |
|---|---|---|---|---|---|
| 2 mg | 0.10 mL | 10 units | Yes | Yes | Yes |
| 4 mg | 0.20 mL | 20 units | Yes | Yes | Yes |
| 8 mg | 0.40 mL | 40 units | No | Yes | Yes |
| 9 mg | 0.45 mL | 45 units | No | Yes | Yes |
| 12 mg | 0.60 mL | 60 units | No | No | Yes |
How long a vial lasts
Whole doses in one vial. The row for the size picked above is marked.
| Vial | 2 mg | 4 mg | 8 mg | 9 mg | 12 mg |
|---|---|---|---|---|---|
| 10 mg vial | 5 doses | 2 doses | 1 dose | 1 dose | Not enough |
| 30 mg vial | 15 doses | 7 doses | 3 doses | 3 doses | 2 doses |
How to mix a Retatrutide vial
These steps are for the 30 mg vial picked in the chart. Change the size there and the amounts here change with it.
- Wash your hands. Wipe the stopper of the peptide vial and the water vial with an alcohol swab.
- Draw 1.5 mL of bacteriostatic water into a syringe.
- Push the needle through the stopper of the peptide vial and let the water run slowly down the glass, not straight onto the powder.
- Swirl the vial gently until the powder is gone. Do not shake it.
- Write the date and 20 mg/mL on the vial, then put it in the fridge.
| Vial | Bacteriostatic water | Concentration |
|---|---|---|
| 10 mg vial | 1 mL | 10 mg/mL |
| 30 mg vial | 1.5 mL | 20 mg/mL |
What Retatrutide is
Retatrutide is an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1 and glucagon receptors, studied as a once-weekly injection for obesity. [1]
Other names: LY3437943.
How it has been given to people: subcutaneous injection, once weekly.
What to know before reading a dose
- Not an approved medicine in the US or Canada as of the check date. Every dose on record is a trial dose.
Doses on record for Retatrutide
Every dose below was given in a human study or printed on an approved label, and each links to its source. Doses set by body weight are left that way.
| From | Where it was used | Dose | How often | For how long | Source |
|---|---|---|---|---|---|
| Human study | Phase 2 obesity trial | 1 mg | once weekly | 48 weeks | [1] |
| Human study | Phase 2 obesity trial, starting dose | 2 mg | once weekly | initial dose before stepping up | [1] |
| Human study | Phase 2 obesity trial | 4 mg | once weekly | 48 weeks | [1] |
| Human study | Phase 2 obesity trial | 8 mg | once weekly | 48 weeks | [1] |
| Human study | Phase 2 obesity trial | 12 mg | once weekly | 48 weeks | [1] |
| Human study | Phase 3 TRIUMPH-1 | 4 mg | once weekly | 80 weeks | [2] |
| Human study | Phase 3 TRIUMPH-1 | 9 mg | once weekly | 80 weeks | [2] |
| Human study | Phase 3 TRIUMPH-1 | 12 mg | once weekly | 80 weeks | [2] |
What the evidence shows
Each finding is tagged by the kind of study it comes from. Human trials are listed first.
Side effects and warnings
Reported in human studies or on a label:
- The most common adverse events were gastrointestinal, dose-related and mostly mild to moderate. Starting at 2 mg instead of 4 mg partly reduced them. [1]
- Heart rate rose with dose, peaked at 24 weeks and fell after that. [1]
Retatrutide has no approved label in the US or Canada for this use, so there is no official list of who should not use it, no interaction list and no missed-dose rule.
Storage
Keep an unmixed vial the way its label says. Once it is mixed, keep it in the fridge, do not freeze it, and write the mixing date on the vial.
Retatrutide dosage questions
How many units is 4 mg of Retatrutide from a 30 mg vial?
Mixed with 1.5 mL of bacteriostatic water, a 30 mg vial is 20 mg/mL. 4 mg is 0.20 mL, which is 20 units on a U-100 syringe.
How much water goes in a 30 mg Retatrutide vial?
1.5 mL gives 20 mg/mL. At that strength the doses in the chart sit at 10, 20, 40, 45, 60 units on a U-100 syringe.
How many doses are in a 30 mg vial?
Whole doses in one vial: 15 at 2 mg, 7 at 4 mg, 3 at 8 mg, 3 at 9 mg, 2 at 12 mg.
Is Retatrutide approved in the US?
Not FDA approved. Drugs@FDA has no retatrutide application, and FDA states that retatrutide is not a component of an FDA-approved drug and cannot be used in compounding.
Is Retatrutide authorized in Canada?
No retatrutide product is in the Health Canada Drug Product Database. Health Canada lists retatrutide among unauthorized injectable peptide drugs it has seized.
What is the half-life of Retatrutide?
About 6 days, from a 12-week phase 1b trial of once-weekly dosing in people with type 2 diabetes (72 enrolled).
What human dosing data is there for Retatrutide?
Not an approved medicine in the US or Canada as of the check date. Every dose on record is a trial dose.
Sources
Each one was opened on 10 Oct 2026 and matched to the line it supports.
- Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med 2023. PubMed 37366315. Trial NCT04881760.
- Jastreboff AM et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med 2026. PubMed 42814954. Trial NCT05929066.
- Urva S et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet 2022. PubMed 36354040. Trial NCT04143802.
Looked for and not found
- No approved label, so no official contraindications, interaction list, missed-dose rule or storage instructions.
- A half-life figure from the phase 1 single ascending dose study. Its abstract (PMID 35985340) says only that the pharmacokinetic profile supported once-weekly dosing.
Change log
10 Oct 2026Page published. 3 sources checked. Vial math added for the 10 and 30 mg vials.
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