Retatrutide Reconstitution: Water, mg/mL and Units per Vial

Water volume, concentration and U-100 syringe units for 5, 10 and 20 mg retatrutide vials, with the phase 2 and TRIUMPH-1 trial amounts as the sources.

Medibact Guides · Published 2026-09-18

Illustration: A clear glass vial with pale blue liquid next to a vial of white lyophilized powder on a white bench. — Illustration

Retatrutide is a triple agonist of the GIP, GLP-1 and glucagon receptors, developed by Eli Lilly under the code LY3437943. It is not approved anywhere, so there is no label, no approved concentration and no labelled volume; the only sourced amounts are the ones its trials used. The lyophilized vial sold on the research market comes, as the calculator notes on this site put it, in sizes that commonly range from 5 to 20 mg, with labelled amounts that vary more between suppliers than for established compounds. This page does the arithmetic for those vials and reports the trial amounts beside it. It recommends nothing.

The retatrutide calculator runs the same sums for any vial and volume, the retatrutide dosage page reports the figures and their sources in full, and the reconstitution hub indexes every compound this site covers.

The arithmetic in one line

Concentration in mg/mL is the vial amount divided by the water volume. Units on a U-100 syringe are the amount in milligrams divided by the concentration, times 100, because a U-100 syringe holds 100 units in 1 mL and every small notch on a standard 1 mL insulin syringe is 1 unit (MedlinePlus, "Giving an insulin injection", reviewed 2024-07-21).

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Water volume per vial size

Vial	1 mL of water	2 mL of water	3 mL of water
5 mg	5 mg/mL	2.5 mg/mL	1.67 mg/mL
10 mg	10 mg/mL	5 mg/mL	3.33 mg/mL
20 mg	20 mg/mL	10 mg/mL	6.67 mg/mL

Units for the trial amounts

The amounts are the ones the trials name. The phase 2 obesity trial used 1, 4, 8 and 12 mg once weekly, with the 4 mg and 8 mg groups started at 2 mg or 4 mg (New England Journal of Medicine, 2023-08-10, PMID 37366315). TRIUMPH-1 used 4, 9 and 12 mg, reached from a 2 mg start through steps at 4, 6 and 9 mg every four weeks (Eli Lilly, 2026-05-21). So the amounts a reader meets in the sources are 1, 2, 4, 6, 8, 9 and 12 mg.

Concentration	1 mg	2 mg	4 mg	6 mg	8 mg	9 mg	12 mg
1.67 mg/mL	60 units	120	240	360	480	540	720
2.5 mg/mL	40	80	160	240	320	360	480
3.33 mg/mL	30	60	120	180	240	270	360
5 mg/mL	20	40	80	120	160	180	240
6.67 mg/mL	15	30	60	90	120	135	180
10 mg/mL	10	20	40	60	80	90	120
20 mg/mL	5	10	20	30	40	45	60

Anything over 100 units exceeds one U-100 syringe. The pattern is the reverse of a microgram peptide: retatrutide's trial amounts are whole milligrams, so dilute solutions run out of syringe quickly. At 2.5 mg/mL, a 5 mg vial in 2 mL, even 4 mg is 160 units; at 10 mg/mL, a 10 mg vial in 1 mL, every trial amount up to 9 mg fits in one syringe and 12 mg needs two draws. The vial also runs out: a 5 mg vial holds one 4 mg amount with 1 mg left, and a 20 mg vial holds five 4 mg amounts or one 12 mg amount with 8 mg left, whatever the water volume.

What "how to mix retatrutide" means in practice

The searches for this page ask for mixing instructions, and the honest answer is that no label gives any, because no product exists to carry one. The steps that approved lyophilized peptide labels describe are the same from product to product: the diluent is added to the vial, the vial is rolled gently between the hands rather than shaken, and the solution is inspected and used only if clear, colourless and free of particles (Egrifta SV label, DailyMed, revised 03/2024, read 2026-09-18; the Zadaxin label, read the same day, adds that reconstitution happens immediately before use). The general procedure for a peptide vial, with the supplies and the order of operations, is Medibact's how to reconstitute peptides; this page does not rewrite it.

The DailyMed listings, and why they are not a label

A DailyMed search for retatrutide on 2026-09-18 returned ten records, which can look as if an approved product exists. It does not. All ten were filed by Guangzhou Yixin Cross-border E-commerce Co., Ltd. under the marketing category "export only", a self-filed listing category that involves no FDA review of safety, effectiveness or labelling; one of them describes a 10 mg lyophilized kit with 1 mL of sterile water and reads like a consumer label. DailyMed publishes what registrants submit. A page that quoted those listings as an approved dose would be quoting the filer, not a regulator.

Storage after mixing

No label states a storage period for a reconstituted retatrutide vial, because no label exists; storage after mixing is covered by Medibact's how to store peptides, which this page links rather than expands.

What the figures omit

Every trial amount above carries a route (subcutaneous), a frequency (once weekly), an escalation interval (four weeks in TRIUMPH-1) and a population (adults meeting each trial's entry criteria, with or without type 2 diabetes). The phase 2 trial reported that gastrointestinal events were dose-related and partially mitigated by the lower 2 mg starting dose (PMID 37366315); TRIUMPH-1 reported 19.0%, 25.9% and 28.3% mean weight loss at 80 weeks for 4, 9 and 12 mg, and 30.3% for the 12 mg group at 104 weeks (Eli Lilly, 2026-05-21); TRANSCEND-T2D-1 studied 4, 9 and 12 mg for 40 weeks in 537 adults with type 2 diabetes (The Lancet, 2026-06-13, PMID 42250575). ClinicalTrials.gov listed 33 studies with retatrutide as an intervention and PubMed held 181 records on 2026-09-18. None of it states a concentration for a research vial or an amount to be drawn from it; the tables convert milligrams to units and stop there. The mechanism, evidence and sourcing belong to Medibact's retatrutide guide, and the store's tirzepatide vs retatrutide comparison sets the two compounds side by side.

Sources and dates

Opened 2026-09-18: DailyMed, retatrutide search (ten "export only" records from one filer) and SPL 425d04f6-6fb2-5c7a-e063-6394a90aa87d; ClinicalTrials.gov v2 API (33 interventional registrations); PubMed (181 records; the abstracts of PMIDs 37366315 and 42250575 read in full); Eli Lilly's TRIUMPH-1 press release of 2026-05-21; MedlinePlus, "Giving an insulin injection" (reviewed 2024-07-21); the Egrifta SV and Zadaxin labels for the mixing description. Vial sizes are the ones the calculator preset uses.

This page does not recommend a dose, a water volume, a syringe or a schedule, and it does not say what any figure means for a particular person. It reports what the trials state, explains why the only listings that look like labels are not, and converts milligrams into millilitres and units.

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Medibact Guides facts

No retatrutide product is approved anywhere as of 2026-09-18; the ten DailyMed records a search returns were filed by a Guangzhou e-commerce company under the 'export only' marketing category, which is a self-filed listing and not an FDA approval (DailyMed SPL 425d04f6-6fb2-5c7a-e063-6394a90aa87d, read 2026-09-18).
A 10 mg retatrutide vial with 1 mL of bacteriostatic water gives 10 mg/mL, so 2 mg is 20 units on a U-100 syringe and 12 mg is 120 units, more than one syringe holds; with 2 mL the vial gives 5 mg/mL and 2 mg is 40 units (arithmetic on the U-100 scale, MedlinePlus, reviewed 2024-07-21).
The phase 2 obesity trial randomised 338 adults to retatrutide 1, 4, 8 or 12 mg once weekly or placebo for 48 weeks, with the 4 and 8 mg groups started at 2 or 4 mg, and reported weight changes at 48 weeks of -8.7%, -17.1%, -22.8% and -24.2% against -2.1% (New England Journal of Medicine, 2023-08-10, PMID 37366315).
TRIUMPH-1 (NCT05929066) studied 4, 9 and 12 mg once weekly in 2,339 adults; treatment began at 2 mg and rose every four weeks through 4, 6 and 9 mg to the target, and the 12 mg group lost 28.3% of body weight at 80 weeks (Eli Lilly press release, 2026-05-21, read 2026-09-18).
TRANSCEND-T2D-1 randomised 537 adults with type 2 diabetes to retatrutide 4, 9 or 12 mg once weekly or placebo for 40 weeks (The Lancet, 2026-06-13, PMID 42250575).
ClinicalTrials.gov listed 33 studies with retatrutide as an intervention and PubMed held 181 records, seven of them tagged as clinical trials, on 2026-09-18.
Retatrutide research vials commonly range from 5 to 20 mg, and labelled amounts vary more between suppliers than for established compounds (calculator notes on this site, ported 2026-09-17).
No label states a storage period for reconstituted retatrutide because no label exists; the storage question is answered by Medibact's storage article, not by this page.

Frequently asked questions

How is retatrutide reconstituted?

By the same arithmetic as any lyophilized peptide: the milligrams on the vial divided by the millilitres of bacteriostatic water added give the concentration, and the concentration sets the syringe units for any amount. A 10 mg vial in 2 mL is 5 mg/mL, so 1 mg is 20 units and 4 mg is 80 units. The physical steps that approved lyophilized peptide labels describe, diluent added to the vial, gentle rolling rather than shaking, a clear solution checked for particles, are set out on Medibact's reconstitution article, which this page links rather than rewrites.

How much bacteriostatic water is mixed with retatrutide?

There is no labelled volume, because there is no label. The volume decides only the concentration. At 1 mL a 5 mg vial is 5 mg/mL, a 10 mg vial 10 mg/mL and a 20 mg vial 20 mg/mL; at 2 mL each is half that; at 3 mL a third. The trial amounts read differently at each: 2 mg is 20 units at 10 mg/mL, 40 units at 5 mg/mL and 60 units at 3.33 mg/mL. The retatrutide calculator on this site gives the reading for any vial and volume.

What is a retatrutide mixing chart?

A table of vial size against water volume with the concentration in each cell, usually followed by the units that concentration gives for a set of amounts. The chart on this page uses the vial sizes the calculator carries, 5, 10 and 20 mg, the three volumes every calculator page on this site uses, 1, 2 and 3 mL, and the amounts named in the retatrutide trials, 1, 2, 4, 6, 8, 9 and 12 mg. It reports the arithmetic; it is not a schedule.

What retatrutide amounts do the trials report?

The phase 2 obesity trial used 1, 4, 8 and 12 mg once weekly for 48 weeks, with the 4 and 8 mg groups started at either 2 or 4 mg (New England Journal of Medicine, 2023, PMID 37366315). TRIUMPH-1 used 4, 9 and 12 mg once weekly, reached by starting at 2 mg and stepping up every four weeks (Eli Lilly, 2026-05-21). TRANSCEND-T2D-1 used 4, 9 and 12 mg for 40 weeks in adults with type 2 diabetes (The Lancet, 2026-06-13). These are trial protocols in defined populations, reported here as figures, not as a plan.

Is retatrutide approved, and does it have a label?

No product is approved anywhere as of 2026-09-18. DailyMed does return ten retatrutide records, but every one was filed by a Guangzhou e-commerce company under the 'export only' marketing category, a self-filed listing that carries no FDA review; one describes a 10 mg lyophilized kit with 1 mL of sterile water. None is a label in the sense this page uses the word. Phase 3 trials are running under Eli Lilly, and a label will exist only if a product is approved.

How many trial-sized amounts does a retatrutide vial hold?

The vial size decides that, whatever the water volume. A 5 mg vial holds five 1 mg amounts, two 2 mg amounts, or one 4 mg amount with 1 mg left over. A 10 mg vial holds five 2 mg amounts, two 4 mg amounts with 2 mg left, or one 8 mg amount. A 20 mg vial holds five 4 mg amounts, two 9 mg amounts with 2 mg left, or one 12 mg amount with 8 mg left. Water changes the volume each amount occupies, never the count.