Free Calculator

Retatrutide Reconstitution Calculator

Turn a vial size, the bacteriostatic water added and a dose in mg into the exact line on a U-100 syringe. The tool also checks the 28-day discard window, compares water amounts, and can check a dose you already drew. Retatrutide is not FDA approved. This page explains what that means before you rely on any number.

10 mg vial + 1 mL 1 mg = 10 units 10 mg/mL. Each unit holds 0.1 mg

10 mg vial + 2 mL 1 mg = 20 units 5 mg/mL. Each unit holds 0.05 mg

FDA status Investigational Lilly plans to file in early 2027

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Maths only. No dose recommendations
Last updated: September 2026

1 The vial

Amount on the vial label ?

Bacteriostatic water added

U-100 syringe size

2 The dose you were given

Dose per weekly injection ?

This calculator does the arithmetic. It cannot tell you whether a dose is safe or right for you, and it cannot tell you what is really in the vial.

The maths for this vial

Draw to U-100 syringe

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Concentration

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Each 1-unit line holds—

Full doses in vial—

Weekly doses in 28 days—

Left at 28 days—

Where the plunger’s top edge should sit —

Drawn to scale for the barrel you picked. Zero is at the needle end.

Units for other amounts in this vial

Amount	Units	Volume	On your syringe

A conversion table, not a dosing schedule. The amounts are round numbers for reference only.

Retatrutide is an investigational drug. No dose has been approved by the FDA or any major regulator. These results are only as accurate as the vial label, and products sold online are not checked for strength, purity or sterility.

1 Vial and dose

Amount on the vial label

Dose per injection

U-100 syringe size

2 Your ideal line (optional)

I want each dose to land on

units

The water only changes how many units a dose takes up. It never changes how much drug is in the vial.

Water amounts compared

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Water	Concentration	1 unit holds	Your dose	How easy to measure

How the Retatrutide Calculator Works

The calculator turns three numbers into a syringe reading. These are the amount of drug in the vial, the water added, and the dose in mg. It has three tabs.

Tab 1: Dose to units

Enter the amount on the vial label, in mg.
Enter the bacteriostatic water added, in mL.
Pick your U-100 syringe size. Smaller barrels are easier to read for small volumes.
Enter the dose you were given, in mg or mcg.
Read the results. You get the unit line, a to-scale syringe picture, how many doses the vial holds, and how many can be used before the 28-day discard date.

Tab 2: How much water?

This compares water amounts from 0.5 to 5 mL for your vial and dose. It shows which ones put the dose on a clean, readable line. It also works out the exact water needed for a unit line you choose.

Tab 3: Check a dose

This works backwards. Enter how the vial was mixed and how many units were drawn, and it shows how many mg that really is. It compares that with the dose you meant to take. This is the check that catches the most common and most dangerous error: using a unit number meant for a different mix.

What Is Retatrutide?

Retatrutide (research code LY3437943) is an investigational weight-loss drug made by Eli Lilly. It is given as an injection under the skin once a week.

It is often called a “triple agonist”. That means it acts on three hormone receptors at once:

GLP-1, the same target as semaglutide (Wegovy). It reduces appetite and slows stomach emptying.
GIP, the second target of tirzepatide (Zepbound). It adds to the effect on appetite and blood sugar.
Glucagon, which is new for this class. Researchers think it may raise energy use and help the body burn fat.

Being “the next step after tirzepatide” is why retatrutide gets so much attention online. That attention has grown much faster than the approval process.

Is Retatrutide FDA Approved?

No. As of September 2026, retatrutide has not been approved by the FDA or any other major regulator, including the UK’s MHRA, Health Canada and Australia’s TGA. It is only available legally inside clinical trials.

Filing timeline. In July 2026, Lilly said it plans to submit retatrutide to the FDA in the first quarter of 2027. FDA review usually takes months after that, so approval is not expected before then.
No legal compounded version. US pharmacies can generally only compound from ingredients that are in approved drugs or on official lists. Retatrutide is neither.
Online “research” vials are unapproved drugs. In a March 2026 warning letter to an online seller, the FDA named retatrutide. It said labels such as “Research Use Only” and “not intended for human consumption” do not change the fact that the products were sold as drugs for people.

What this means for the calculator

Every result depends on the vial containing exactly what its label says. With unapproved products, nobody has checked that. The FDA warns that unapproved GLP-1 products may contain the wrong ingredient, too much, too little or none at all.

Retatrutide Clinical Trials

Most competitor pages quote only the 2023 phase 2 study. Several large phase 3 trials have reported since then. Here is where the evidence stands.

Trial	Who took part	Weekly doses	Length	Average weight loss
Phase 2 (NEJM, 2023)	338 adults with obesity, no diabetes	1, 4, 8, 12 mg	48 weeks	8.7% to 24.2% (placebo 2.1%)
TRIUMPH-4 (Dec 2025)	445 adults with obesity and knee arthritis	9, 12 mg	68 weeks	26.4% and 28.7% (placebo 2.1%)
TRIUMPH-1 (May 2026)	2,339 adults with obesity, no diabetes	4, 9, 12 mg	80 weeks	19.0% to 28.3% (placebo 2.2%). 30.3% at 104 weeks on 12 mg
TRIUMPH-2 (Jul 2026)	1,152 adults with type 2 diabetes and obesity	4, 9, 12 mg	80 weeks	Up to 20.8%. A1C down up to 1.6%
TRIUMPH-3 (Jul 2026)	1,949 adults with severe obesity and heart disease	9, 12 mg	80 weeks	Up to 22.6%

Three things these headline numbers do not tell you:

Most phase 3 results are company announcements. They have not all been published in full, peer-reviewed papers yet.
Doses were increased slowly, under medical supervision. Participants started low and moved up in steps, with regular check-ups. Trial doses are not a home protocol.
The trial drug was made by Lilly. It was produced to pharmaceutical standards. Results from trials say nothing about what is in a vial bought online.

Retatrutide Concentration and Reconstitution Mathematics

The maths has three steps and works for any powdered peptide.

1. Concentration (mg/mL) = vial mg ÷ water mL
2. Volume (mL) = dose mg ÷ concentration
3. Units on a U-100 syringe = volume × 100

Example: a 10 mg vial with 2 mL of water is 5 mg/mL. A 1 mg dose is 1 ÷ 5 = 0.2 mL, which is 20 units. The same 1 mg from the same vial mixed with 1 mL of water is only 10 units.

Retatrutide reconstitution chart

This chart shows how the same amounts change with the mix. It is a conversion reference, not a dose guide.

Vial + water	Concentration	1 unit holds	1 mg	2 mg	5 mg
5 mg + 1 mL	5 mg/mL	0.05 mg	20 units	40 units	100 units
10 mg + 1 mL	10 mg/mL	0.1 mg	10 units	20 units	50 units
10 mg + 2 mL	5 mg/mL	0.05 mg	20 units	40 units	100 units
12 mg + 2 mL	6 mg/mL	0.06 mg	16.7 units	33.3 units	83.3 units
20 mg + 2 mL	10 mg/mL	0.1 mg	10 units	20 units	50 units
30 mg + 2 mL	15 mg/mL	0.15 mg	6.7 units	13.3 units	33.3 units
30 mg + 3 mL	10 mg/mL	0.1 mg	10 units	20 units	50 units

Two patterns worth knowing. At 10 mg/mL, 1 mg is always 10 units, which makes errors easier to spot. Mixes such as 12 mg in 2 mL give results like 16.7 units that fall between lines and have to be rounded.

The 28-day limit

Bacteriostatic water contains a preservative, but a punctured multi-dose vial is not sterile forever. The FDA’s advice for multi-dose GLP-1 vials is to discard them within 28 days of first use. At one injection a week, that is 4 doses. Some sites recommend large vials “to save money”, but a big vial at a small dose can leave most of it past its discard date. Tab 1 shows this for your numbers.

Reconstitution vs. Dosing

These are two separate questions. Many retatrutide pages blur them together.

	Reconstitution	Dosing
The question	How many units hold X mg in this vial?	How many mg should this person take?
Answered by	Arithmetic	A clinician, using approved labelling and your health history
For retatrutide	This calculator can do it	No approved dose exists yet

That is why this calculator has no dose presets or titration schedule. Some competitors call the phase 2 starting step the “consensus starting dose”. It isn’t. It was one arm of a supervised study. A preset button would look like a recommendation, and there is no approved dose to recommend.

Safety Information

Side effects seen in trials

Stomach and gut effects were the most common. In TRIUMPH-1, nausea affected 28.6% to 42.4% of people and diarrhoea 25.2% to 34.1%, depending on dose. Constipation and vomiting were also common.
Dysaesthesia means unusual skin sensations such as tingling, burning or sensitivity. It was reported in 5.1% to 12.5% of people in TRIUMPH-1, and in 20.9% at 12 mg in TRIUMPH-4, compared with under 1% on placebo. It was mostly mild.
Stopping because of side effects ranged from 4.1% to 11.3% across doses in TRIUMPH-1, and was 18.2% at 12 mg in TRIUMPH-4.
Heart outcomes are not settled. TRIUMPH-3 was not designed to test heart benefit. It recorded 27 major cardiovascular events on retatrutide compared with 23 on placebo.

Risks outside a trial

Unknown contents. Unapproved vials may be under-filled, over-filled, contaminated or not retatrutide at all.
No medical screening. Trials excluded people with certain conditions and monitored the rest closely.
Unknown class risks. Approved drugs in this family carry a boxed warning about thyroid C-cell tumours in rodents, and warnings about pancreatitis and gallbladder disease. Whether these apply to retatrutide is still being studied.
Pregnancy. There is no safety data for pregnancy or breastfeeding.
Hygiene. Use a new sterile needle every time, never share needles, and get rid of sharps safely.

Interested in retatrutide? The only legal way to use it right now is in a clinical trial. You can search for trials near you on ClinicalTrials.gov. Approved alternatives such as tirzepatide and semaglutide are available on prescription.

Common Calculation Mistakes

Reusing a unit number from someone else’s mix. “20 units” means 1 mg in one vial and 2 mg in another. Always calculate from your own vial and water.
Treating units as mg. 10 units is a volume of 0.1 mL, not 10 mg. The FDA has reported 5 to 20 times overdoses from this kind of mix-up with compounded semaglutide.
Mixing up mg and mcg. 1 mg = 1,000 mcg. A slip here is a thousandfold error.
Forgetting how much water was added. Write it on the vial straight away. The “Copy vial label” button gives you the text.
Rounding a between-lines dose without noticing. 16.7 units is not 17 units on every syringe. Use Tab 2 to pick a mix that lands on whole lines.
Keeping a vial past 28 days because there is drug left in it.
Using a U-40 syringe. These are for pet insulin and give 2.5 times the volume per unit. See our units to mL calculator.

Frequently Asked Questions

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

There is no official figure, because retatrutide has no approved label. The water only sets the concentration. With 1 mL, the vial is 10 mg/mL and 1 mg is 10 units. With 2 mL, it is 5 mg/mL and 1 mg is 20 units. The “How much water?” tab compares options for a given amount.

How many units is 1 mg of retatrutide?

It depends entirely on the mix. At 10 mg/mL it is 10 units. At 5 mg/mL it is 20 units. At 6 mg/mL (12 mg in 2 mL) it is about 16.7 units. There is no fixed answer.

Is retatrutide FDA approved?

No. As of September 2026 it is investigational. Lilly has said it plans to submit it to the FDA in the first quarter of 2027. Until approval, it is only legally available in clinical trials.

Is research-grade retatrutide legal to buy?

The FDA treats retatrutide sold online for human use as an unapproved drug, even when labelled “research use only”. It has sent warning letters to sellers. These products are not tested for strength, purity or sterility.

How long does reconstituted retatrutide last?

No stability data for mixed retatrutide has been published. The FDA’s general advice for multi-dose GLP-1 vials is to discard them within 28 days of first use. That is best treated as a maximum, not a target.

What doses were used in retatrutide trials?

The phase 2 trial tested 1, 4, 8 and 12 mg once weekly. Phase 3 TRIUMPH trials tested 4, 9 and 12 mg. Doses were increased gradually under medical supervision. These are research doses, not approved or recommended doses.

Does this calculator store my information?

No. Everything runs in your browser. Nothing is sent, saved or shared.

Sources and References

Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389:514–526. nejm.org
Eli Lilly and Company. Retatrutide TRIUMPH-4 topline results. December 11, 2025. investor.lilly.com
Eli Lilly and Company. Retatrutide TRIUMPH-1 topline results. May 21, 2026. investor.lilly.com
Eli Lilly and Company. Retatrutide TRIUMPH-2 and TRIUMPH-3 topline results. July 23, 2026. investor.lilly.com
BioPharma Dive. Lilly, with new data, to seek FDA approval of obesity drug retatrutide. July 2026. biopharmadive.com
US Food and Drug Administration. Warning letter: Gram Peptides (MARCS-CMS 721806). March 31, 2026. fda.gov
US Food and Drug Administration. FDA’s concerns with unapproved GLP-1 drugs used for weight loss. Updated September 2026. fda.gov

Reviewed and updated: September 2026. Retatrutide’s status is changing quickly. We update this page when new trial results or regulatory decisions are published.