Not FDA-approvedRetatrutide is an investigational drug from Eli Lilly. It is not approved anywhere in the world, and the FDA says it cannot be used in compounding.[4][5] This calculator does arithmetic only. It does not recommend a dose.
How to use the calculator
- Peptide in the vial: the total milligrams printed on the label (for example 10 mg).
- Water added: how many millilitres of diluent went into that vial (for example 2 mL).
- Dose: the dose you were told to measure, in mg or mcg.
- Syringe: the size of your U-100 insulin syringe. The calculator warns you if the dose does not fit.
The result is the number of units to draw. In the example, 10 mg in 2 mL is 5 mg per mL. A 2 mg dose is 0.4 mL, which is 40 units on a U-100 syringe. The reconstitution guide explains each step and how the water volume changes the numbers.
Retatrutide dosage for weight loss in clinical trials
All retatrutide trials gave the drug once a week as an injection under the skin.[1] The dose is never started high. It is raised step by step every 4 weeks to reduce stomach side effects.
| Target dose | Steps, every 4 weeks | Reached from |
|---|---|---|
| 4 mg | 2 → 4 mg | Week 5 |
| 9 mg | 2 → 4 → 6 → 9 mg | Week 13 |
| 12 mg | 2 → 4 → 6 → 9 → 12 mg | Week 17 |
The phase 2 obesity trial also tested 1 mg and 8 mg arms, and a 12 mg arm that went 2 → 4 → 8 → 12 mg.[1] Week numbers in the table above are simple arithmetic from the 4-week steps. The full schedules, with the trial each one comes from, are in the retatrutide dosage chart.
Retatrutide dose in units for each trial step
These two tables use the most common round-number mixes. If your vial or water amount is different, use the calculator above.
| Dose | Units (U-100) | mL | Doses per vial |
|---|---|---|---|
| 1 mg | 20 | 0.2 | 10 |
| 2 mg | 40 | 0.4 | 5 |
| 4 mg | 80 | 0.8 | 2.5 |
| 6 mg | 120 | 1.2 | 1.7 |
| 8 mg | 160 | 1.6 | 1.3 |
| 9 mg | 180 | 1.8 | 1.1 |
| Dose | Units (U-100) | mL | Doses per vial |
|---|---|---|---|
| 1 mg | 10 | 0.1 | 10 |
| 2 mg | 20 | 0.2 | 5 |
| 4 mg | 40 | 0.4 | 2.5 |
| 6 mg | 60 | 0.6 | 1.7 |
| 8 mg | 80 | 0.8 | 1.3 |
| 9 mg | 90 | 0.9 | 1.1 |
A 12 mg dose is more than a 10 mg vial holds. For larger vials see the 20 mg, 24 mg and 30 mg guides.
What the trials found, in one paragraph
In TRIUMPH-1, the main phase 3 obesity trial with 2,339 adults, people on 12 mg lost an average of 25.0% of body weight at 80 weeks in the journal's primary analysis, against 3.9% on placebo. Counting only people who stayed on treatment, the figure was 28.3%.[3][2] Stomach side effects were common and rose with dose. See results and side effects for the full numbers.
Guides on this site
- Retatrutide dosage chartEvery escalation schedule used in trials
- Reconstitution mathHow water volume changes units per dose
- Dose in units and mLConversion charts and a reverse calculator
- Side effectsRates by dose from phase 2 and phase 3
- FDA approval statusWhere the drug stands and what comes next
- Eli Lilly early accessWho qualifies for the pre-approval program
- How to get retatrutideTrials, early access and approval
- Lawsuits and enforcementLilly v. sellers, Lilly v. FDA
- Retatrutide vs tirzepatideWhat the separate trials show
- Retatrutide vs semaglutideThe head-to-head result
- Results by doseWeight loss in every trial
- Clinical trials trackerAll 33 studies and their status
- Half-lifeAbout 6 days, and what that means
- Mechanism of actionGIP, GLP-1 and glucagon receptors
- Skin sensitivityDysesthesia rates by trial
- Heart rate and blood pressureWhat the trials measured
- What is retatrutide?The triple agonist, explained
- Retatrutide costWhy there is no official price yet
- Retatrutide peptide sold onlineWhat the FDA has said about sellers
Frequently asked questions
How many units is 2 mg of retatrutide?
It depends on the concentration in your vial. At 5 mg/mL (10 mg in 2 mL) it is 40 units. At 10 mg/mL (10 mg in 1 mL) it is 20 units. Enter your own numbers in the calculator.
What is the starting dose of retatrutide?
What is the retatrutide dosage in trials?
Once weekly, starting at 2 mg and rising every 4 weeks to a maintenance dose of 4, 9 or 12 mg in phase 3.[3] The full week-by-week schedule is on the retatrutide dosing page.
What is the highest dose of retatrutide studied?
Is retatrutide available by prescription?
No. As of November 2026 it is not approved by the FDA or any other regulator. Lilly plans to submit it for U.S. approval in the first quarter of 2027.[4] See FDA approval status.
Does this calculator work for other peptides?
The math is the same for any powder mixed with water and measured on a U-100 syringe. The preset buttons on this page are set to the doses used in retatrutide trials.
Sources
- Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial
- Lilly: retatrutide delivered powerful weight loss in pivotal phase 3 obesity trial (TRIUMPH-1)
- Jastreboff AM et al. Retatrutide for obesity (TRIUMPH-1)
- Lilly: retatrutide vs semaglutide 2 mg in TRANSCEND-T2D-2
- FDA's concerns with unapproved GLP-1 drugs used for weight loss
- Retatrutide studies (NCT04881760, NCT05929066, NCT05931367, NCT06662383, NCT07629401 and others)