Is retatrutide FDA approved?

No. Retatrutide is investigational and has no marketing authorisation from the FDA, the EMA or any other regulator, anywhere in the world, for any indication. As of 2026 it remains in Eli Lilly’s clinical programme following the 338-participant phase 2 obesity trial published in the New England Journal of Medicine in 2023. There is no approved label, no approved dose, and no lawful route to a prescription for it. Material sold online is not a medicine and is typically labelled “for research use only”, which means it has not been manufactured, tested or released to pharmaceutical standards.

How do you calculate a retatrutide dose in units?

Divide the vial mass by the bacteriostatic water you added to get the concentration, divide your dose by that concentration to get the volume, then multiply by 100 because a U-100 syringe is graduated so 100 units equals 1 mL. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL, so a 4 mg dose is 0.80 mL — 80 units. One unit delivers 0.05 mg at that concentration.

How much bacteriostatic water do you add to a 10 mg retatrutide vial?

There is no correct answer, because there is no label — the water volume only sets the concentration, and the milligrams in the vial do not change. Adding 1 mL gives 10 mg/mL, so a 4 mg dose is 40 units. Adding 2 mL gives 5 mg/mL and the same dose becomes 80 units. More water makes small doses easier to measure accurately on the barrel; less water keeps the injection volume down. Both deliver identical milligrams.

What doses of retatrutide were used in clinical trials?

In the phase 2 obesity trial, 338 adults received subcutaneous retatrutide once weekly at maintenance doses of 1 mg, 4 mg, 8 mg or 12 mg for 48 weeks, starting at 2 mg or 4 mg and escalating stepwise. The phase 2 type 2 diabetes trial published in the Lancet studied 0.5, 4, 8 and 12 mg on the same weekly schedule. These are doses that were administered under trial supervision with monitoring and eligibility screening — they are a record of what was studied, not a dosing recommendation.

How many units is 8 mg of retatrutide?

It depends entirely on the concentration, which is why the question has no single answer. At 5 mg/mL it is 160 units (1.60 mL); at 10 mg/mL, 80 units (0.80 mL); at 15 mg/mL, 53.25 units (0.53 mL). Anyone quoting a unit figure without stating the concentration is quoting a number that is meaningless for your vial.

How long does a retatrutide vial last?

Vial mass divided by dose, rounded down, and the water volume makes no difference to it. A 10 mg vial gives 2 whole 4 mg doses — 2 weeks on a weekly schedule. A 30 mg vial gives 3 whole 8 mg doses. Note that this is arithmetic about contents, not about stability: a reconstituted peptide has a limited shelf life once water is added, and no beyond-use date has been established for an unapproved compound.

Is retatrutide stronger than tirzepatide or semaglutide?

The trials were not head to head, so the honest answer is that nobody knows. In its 48-week phase 2 obesity trial retatrutide produced a least-squares mean weight change of −22.8% at 8 mg and −24.2% at 12 mg, against −2.1% for placebo. Those figures look larger than the published trials of approved agents, but comparing across different trials with different populations and durations is not a valid comparison, and no trial has yet compared them directly. Semaglutide and tirzepatide also have phase 3 safety data and regulatory review behind them; retatrutide does not.

What side effects were reported in the retatrutide trials?

The most common adverse events in the phase 2 obesity trial were gastrointestinal — nausea, diarrhoea and vomiting. They were dose-related, mostly mild to moderate, and were partially mitigated by starting at 2 mg rather than 4 mg. The trial also recorded dose-dependent increases in heart rate that peaked at 24 weeks and declined afterwards. This is what was observed in 338 supervised participants over 48 weeks; it is not a complete safety profile, because an investigational compound does not have one.

Investigational compound — not approved anywhere

Retatrutide Dosage Calculator

Convert a retatrutide dose in milligrams into units on a U-100 syringe from your vial size and the bacteriostatic water you added — with the full reconstitution chart below.

Reviewed by: Alpha Health Finder Editorial Team
Last reviewed: September 2026

What retatrutide is, and what this calculator does not do

Retatrutide (development code LY3437943) is an investigational once-weekly peptide that activates three receptors at once: GIP, GLP-1 and glucagon. It is not approved by the FDA, the EMA or any other regulator, for any indication, anywhere in the world. There is no approved label, no approved dose, and no legal route to a prescription for it. Everything published about its dosing comes from clinical trials run by Eli Lilly, and a trial dose administered under study supervision is not a recommendation to anyone outside that trial.

This page exists for one narrow reason. Retatrutide is supplied — where it is supplied at all — as a lyophilised powder in a sealed vial, labelled only with a mass in milligrams. Turning that into a mark on a syringe barrel requires two steps that people get wrong: choosing how much bacteriostatic water to add, which sets the concentration, and then converting a milligram figure into units. A U-100 insulin syringe is graduated so that 100 units equals 1 mL, not 100 mg, and mistaking one for the other is a ten-fold error. Publishing the correct arithmetic is safer than leaving it to a forum post.

What follows converts numbers. It does not tell you what dose to take, it does not suggest that you should take any, and it cannot substitute for a clinician. If you want a weight-loss medicine that has been through the approval process, semaglutide and tirzepatide are approved for chronic weight management and are available on prescription — retatrutide is not.

The formula

concentration (mg/mL) = vial mass (mg) ÷ bacteriostatic water (mL)

volume (mL) = dose (mg) ÷ concentration (mg/mL)

units on a U-100 syringe = volume (mL) × 100

doses per vial = ⌊ vial mass (mg) ÷ dose (mg) ⌋

A U-100 barrel is graduated so that 100 units = 1 mL. The lyophilised cake displaces a negligible volume at these masses, so the final volume is taken to be the volume of water added — the assumption every reconstitution chart makes. Units are rounded to the quarter mark, because that is the finest a barrel can honestly be read to.

Worked example

A 10 mg vial reconstituted with 2 mL of bacteriostatic water, for a 4 mg dose:

Concentration = 10 mg ÷ 2 mL = 5 mg/mL
One unit on the barrel therefore delivers 0.05 mg
Volume = 4 mg ÷ 5 mg/mL = 0.80 mL
Units = 0.80 × 100 = 80 units
The vial holds 2 whole doses of 4 mg — 2 weeks at one injection a week
Had you added only 1 mL instead, the same 4 mg would be 40 units — the dose is identical, the mark on the barrel is not

Retatrutide dosage chart — mg to units on a U-100 syringe

Read down for your dose in milligrams, across for the concentration you reconstituted to. Every cell is units on a U-100 insulin syringe, with the volume beneath.

Dose	2.5 mg/mL5 mg + 2 mL	5 mg/mL10 mg + 2 mL	7.5 mg/mL15 mg + 2 mL	10 mg/mL10 mg + 1 mL	15 mg/mL30 mg + 2 mL
0.5 mg	20 u0.20 mL	10 u0.10 mL	6.75 u0.07 mL	5 u0.05 mL	3.25 u0.03 mL
1 mg	40 u0.40 mL	20 u0.20 mL	13.25 u0.13 mL	10 u0.10 mL	6.75 u0.07 mL
2 mg	80 u0.80 mL	40 u0.40 mL	26.75 u0.27 mL	20 u0.20 mL	13.25 u0.13 mL
3 mg	120 u1.20 mL — won't fit	60 u0.60 mL	40 u0.40 mL	30 u0.30 mL	20 u0.20 mL
4 mg	160 u1.60 mL — won't fit	80 u0.80 mL	53.25 u0.53 mL	40 u0.40 mL	26.75 u0.27 mL
6 mg	240 u2.40 mL — won't fit	120 u1.20 mL — won't fit	80 u0.80 mL	60 u0.60 mL	40 u0.40 mL
8 mg	320 u3.20 mL — won't fit	160 u1.60 mL — won't fit	106.75 u1.07 mL — won't fit	80 u0.80 mL	53.25 u0.53 mL
10 mg	400 u4.00 mL — won't fit	200 u2.00 mL — won't fit	133.25 u1.33 mL — won't fit	100 u1.00 mL	66.75 u0.67 mL
12 mg	480 u4.80 mL — won't fit	240 u2.40 mL — won't fit	160 u1.60 mL — won't fit	120 u1.20 mL — won't fit	80 u0.80 mL

Doses of 0.5–12 mg are tabulated because that spans what was administered in the published phase 2 trials; tabulating a figure is not recommending it. A cell marked "won't fit" exceeds the 100 units a 1 mL U-100 barrel holds, which is a signal the reconstitution is too dilute for that dose rather than an instruction to take two injections.

Retatrutide reconstitution chart — vial size and bacteriostatic water

What each vial-and-water combination produces, and the units it puts a given dose at. Find your vial size and the volume you added.

Vial + BAC water	Concentration	1 unit =	2 mgunits	4 mgunits	8 mgunits	12 mgunits
5 mg + 1 mL	5 mg/mL	0.05 mg	40 u2 per vial	80 u1 per vial	160 uvial too small	240 uvial too small
5 mg + 2 mL	2.5 mg/mL	0.025 mg	80 u2 per vial	160 u1 per vial · won't fit	320 uvial too small	480 uvial too small
5 mg + 3 mL	1.67 mg/mL	0.0167 mg	120 u2 per vial · won't fit	240 u1 per vial · won't fit	480 uvial too small	720 uvial too small
10 mg + 1 mL	10 mg/mL	0.1 mg	20 u5 per vial	40 u2 per vial	80 u1 per vial	120 uvial too small
10 mg + 2 mL	5 mg/mL	0.05 mg	40 u5 per vial	80 u2 per vial	160 u1 per vial · won't fit	240 uvial too small
10 mg + 3 mL	3.33 mg/mL	0.0333 mg	60 u5 per vial	120 u2 per vial · won't fit	240 u1 per vial · won't fit	360 uvial too small
15 mg + 1 mL	15 mg/mL	0.15 mg	13.25 u7 per vial	26.75 u3 per vial	53.25 u1 per vial	80 u1 per vial
15 mg + 2 mL	7.5 mg/mL	0.075 mg	26.75 u7 per vial	53.25 u3 per vial	106.75 u1 per vial · won't fit	160 u1 per vial · won't fit
15 mg + 3 mL	5 mg/mL	0.05 mg	40 u7 per vial	80 u3 per vial	160 u1 per vial · won't fit	240 u1 per vial · won't fit
20 mg + 1 mL	20 mg/mL	0.2 mg	10 u10 per vial	20 u5 per vial	40 u2 per vial	60 u1 per vial
20 mg + 2 mL	10 mg/mL	0.1 mg	20 u10 per vial	40 u5 per vial	80 u2 per vial	120 u1 per vial · won't fit
20 mg + 3 mL	6.67 mg/mL	0.0667 mg	30 u10 per vial	60 u5 per vial	120 u2 per vial · won't fit	180 u1 per vial · won't fit
30 mg + 1 mL	30 mg/mL	0.3 mg	6.75 u15 per vial	13.25 u7 per vial	26.75 u3 per vial	40 u2 per vial
30 mg + 2 mL	15 mg/mL	0.15 mg	13.25 u15 per vial	26.75 u7 per vial	53.25 u3 per vial	80 u2 per vial
30 mg + 3 mL	10 mg/mL	0.1 mg	20 u15 per vial	40 u7 per vial	80 u3 per vial	120 u2 per vial · won't fit

Vial masses are the sizes these compounds are commonly supplied in — they are not label strengths, because there is no label. Doses per vial counts whole doses only; a partial dose left in the vial is not a dose. “Won’t fit” marks a draw above the 100 units a 1 mL U-100 barrel holds.

Doses administered in the phase 2 obesity trial

Least-squares mean percentage change in body weight by once-weekly maintenance dose, alongside what each dose is in syringe units at two common concentrations.

Weekly dose	Weight change24 weeks	Weight change48 weeks	Unitsat 5 mg/mL	Unitsat 10 mg/mL
1 mg	-7.2%	-8.7%	20 u0.20 mL	10 u0.10 mL
4 mg	-12.9%	-17.1%	80 u0.80 mL	40 u0.40 mL
8 mg	-17.3%	-22.8%	160 u1.60 mL — won't fit	80 u0.80 mL
12 mg	-17.5%	-24.2%	240 u2.40 mL — won't fit	120 u1.20 mL — won't fit
Placebo	-1.6%	-2.1%	—	—

Doses and outcomes from Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med 2023;389(6):514–526 (PMID 37366315). Retatrutide is investigational and is not approved for use anywhere. The 4 mg and 8 mg rows are the combined arms: each was studied with two different starting doses and the published abstract reports them pooled. The 12 mg arm escalated stepwise through 2 → 4 → 8 → 12 mg; neither the abstract nor the ClinicalTrials.gov record for NCT04881760 states the interval between steps, so none is given here.

Frequently asked questions

Is retatrutide FDA approved?: No. Retatrutide is investigational and has no marketing authorisation from the FDA, the EMA or any other regulator, anywhere in the world, for any indication. As of 2026 it remains in Eli Lilly’s clinical programme following the 338-participant phase 2 obesity trial published in the New England Journal of Medicine in 2023. There is no approved label, no approved dose, and no lawful route to a prescription for it. Material sold online is not a medicine and is typically labelled “for research use only”, which means it has not been manufactured, tested or released to pharmaceutical standards.
How do you calculate a retatrutide dose in units?: Divide the vial mass by the bacteriostatic water you added to get the concentration, divide your dose by that concentration to get the volume, then multiply by 100 because a U-100 syringe is graduated so 100 units equals 1 mL. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL, so a 4 mg dose is 0.80 mL — 80 units. One unit delivers 0.05 mg at that concentration.
How much bacteriostatic water do you add to a 10 mg retatrutide vial?: There is no correct answer, because there is no label — the water volume only sets the concentration, and the milligrams in the vial do not change. Adding 1 mL gives 10 mg/mL, so a 4 mg dose is 40 units. Adding 2 mL gives 5 mg/mL and the same dose becomes 80 units. More water makes small doses easier to measure accurately on the barrel; less water keeps the injection volume down. Both deliver identical milligrams.
What doses of retatrutide were used in clinical trials?: In the phase 2 obesity trial, 338 adults received subcutaneous retatrutide once weekly at maintenance doses of 1 mg, 4 mg, 8 mg or 12 mg for 48 weeks, starting at 2 mg or 4 mg and escalating stepwise. The phase 2 type 2 diabetes trial published in the Lancet studied 0.5, 4, 8 and 12 mg on the same weekly schedule. These are doses that were administered under trial supervision with monitoring and eligibility screening — they are a record of what was studied, not a dosing recommendation.
How many units is 8 mg of retatrutide?: It depends entirely on the concentration, which is why the question has no single answer. At 5 mg/mL it is 160 units (1.60 mL); at 10 mg/mL, 80 units (0.80 mL); at 15 mg/mL, 53.25 units (0.53 mL). Anyone quoting a unit figure without stating the concentration is quoting a number that is meaningless for your vial.
How long does a retatrutide vial last?: Vial mass divided by dose, rounded down, and the water volume makes no difference to it. A 10 mg vial gives 2 whole 4 mg doses — 2 weeks on a weekly schedule. A 30 mg vial gives 3 whole 8 mg doses. Note that this is arithmetic about contents, not about stability: a reconstituted peptide has a limited shelf life once water is added, and no beyond-use date has been established for an unapproved compound.
Is retatrutide stronger than tirzepatide or semaglutide?: The trials were not head to head, so the honest answer is that nobody knows. In its 48-week phase 2 obesity trial retatrutide produced a least-squares mean weight change of −22.8% at 8 mg and −24.2% at 12 mg, against −2.1% for placebo. Those figures look larger than the published trials of approved agents, but comparing across different trials with different populations and durations is not a valid comparison, and no trial has yet compared them directly. Semaglutide and tirzepatide also have phase 3 safety data and regulatory review behind them; retatrutide does not.
What side effects were reported in the retatrutide trials?: The most common adverse events in the phase 2 obesity trial were gastrointestinal — nausea, diarrhoea and vomiting. They were dose-related, mostly mild to moderate, and were partially mitigated by starting at 2 mg rather than 4 mg. The trial also recorded dose-dependent increases in heart rate that peaked at 24 weeks and declined afterwards. This is what was observed in 338 supervised participants over 48 weeks; it is not a complete safety profile, because an investigational compound does not have one.

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Educational reference, not medical advice. Retatrutide is an investigational compound with no marketing authorisation anywhere in the world. Nothing on this page is a dose recommendation, an endorsement, or a suggestion that retatrutide can be lawfully prescribed or obtained. It converts units of measurement for someone who already holds a vial. Discuss any weight-loss medicine with a clinician.