How to Reconstitute Retatrutide (Mixing Chart by Vial Size)

Knowing how to reconstitute retatrutide is mostly arithmetic. The milligrams in the vial divided by the milliliters of bacteriostatic (bac) water you add gives the strength, and the strength decides how many syringe units hold a dose. A 10 mg vial mixed with 1 mL of bac water makes 10 mg per mL, so every 10 units on a U-100 insulin syringe holds 1 mg. The hands-on part is gentle: water in slowly, swirl, never shake, and check that it's clear.

As of September 2026, retatrutide is still in Phase 3 trials, no approved version exists yet, and Lilly says it's legally available only to people in its trials. Lilly hasn't published a mixing recipe, and the TRIUMPH-1 registry entry says only that retatrutide is given under the skin. So a vial of powder bought online sits outside anything Lilly has documented, and the steps below borrow from the label for bac water, the labels of approved injectables and FDA's warnings about vials people measure at home.

What you need before you mix

Work on a clean, well-lit table. This list follows the kit and instructions for Egrifta WR, an approved peptide powder that's mixed with bac water at home. That's tesamorelin's kit, not retatrutide's, but the job is the same.

• The retatrutide vial, with its milligram amount on the label
• Bacteriostatic Water for Injection, USP, in a sealed multi-dose vial
• A mixing syringe big enough for the water volume (Egrifta WR's kit uses a 3 mL syringe for this step)
• U-100 insulin syringes for the doses, one new syringe and needle per injection, as FDA advises
• Alcohol swabs
• A pen for the vial label, and a sharps container

Bac water is sterile water with benzyl alcohol added as a preservative: 0.9% in Hospira's 30 mL vial and 1.1% in its 20 mL glass vial, according to the label. That preservative is why people use it for a vial they'll puncture every week. Plain sterile water has none. The same label warns that some drugs don't get along with benzyl alcohol, and nobody has published whether retatrutide is one of them.

How to reconstitute retatrutide, step by step

These steps follow approved labels, mainly Egrifta WR's, adapted to one retatrutide vial.

1. Wash and dry your hands, then check the powder. It needs to look like a white or off-white cake with no discoloration or loose particles.
2. Check the expiry date on the bac water, and the date you first opened it.
3. Flip off both plastic caps and wipe both rubber stoppers with an alcohol swab. Let them air-dry.
4. Pull the mixing syringe's plunger back to your planned water volume to fill it with air.
5. Push the needle into the bac water vial, inject the air, turn the vial upside down and draw out a little more water than you need.
6. Tap out the big bubbles and push the plunger up to the exact volume.
7. Insert the needle into the retatrutide vial, push the plunger down until the syringe is empty, then pull the needle out.
8. Swirl or roll the vial gently until the powder dissolves. Don't shake it. Egrifta WR's label says the same thing about its peptide.
9. Let it rest for a few seconds so any foam settles, then hold it up to the light.
10. Write the date, the strength and "mixed" on the vial, and keep it in the fridge. That's borrowed from approved GLP-1 injections, which FDA says need refrigeration.

The liquid needs to be clear and colorless with nothing floating in it. The bac water label says to check any mixed drug for clarity and stray particles before use, and Lilly's Zepbound label says not to use tirzepatide with particles or discoloration. If yours is cloudy, stringy or has flecks that don't dissolve after a gentle swirl and a rest, don't inject it; our guide to a cloudy retatrutide vial covers the likely causes.

Retatrutide mixing chart by vial size

Strength (mg per mL) = milligrams in the vial ÷ mL of water. Units to draw = dose in mg ÷ strength × 100. Those two lines are all any reconstitution chart does.

The doses below, 2 mg and 4 mg, are the first two steps used in TRIUMPH-1, where Lilly started everyone at 2 mg and raised the dose every 4 weeks, through 4, 6 and 9 mg for people heading to 12 mg. They're here to show the math, not as advice on what to take.

Two things the chart hides. The simple division is an approximation: Egrifta WR's label puts its 11.6 mg vial mixed with 1.3 mL at 8 mg per mL, not the 8.9 that 11.6 ÷ 1.3 gives, and we couldn't find a comparable figure for any retatrutide vial. And the milligrams on the label are only as good as the vial. If you're comparing retatrutide for sale listings, the math above assumes the vial holds what it says, which only a batch-specific test report can back up. In the Victoria Department of Health's June 2026 alert, still marked active as of September 2026, six people had acute liver injury after using unapproved products labeled retatrutide, and officials said a contaminant was a possible cause.

Our read: pick the water volume that puts your dose well inside the syringe barrel, away from the 5-unit end where FDA's reported misreads happened and short of the 100-unit line. For most vials that means making it 10 mg per mL.

How many units is each dose?

A U-100 insulin syringe holds 1 mL across 100 markings, so each unit is 0.01 mL. FDA's dosing-error alert uses exactly that example: a 5-unit dose is 0.05 mL. Here are the TRIUMPH-1 dose steps at three strengths.

Worked through once: a 20 mg vial mixed with 2 mL is 10 mg per mL, so a 4 mg dose is 4 ÷ 10 = 0.4 mL, or 40 units. The 12 mg row answers a question people search for a lot, "how much bac water for 12 mg": at 10 mg per mL it's 120 units, more than one standard insulin syringe holds, so people either mix a stronger vial or split the dose. Splitting means two needle sticks and two chances to misread.

Units here are marks on a syringe, not a measure of drug. The same 20 units is 1 mg in one vial and 4 mg in another, which is why our retatrutide calculator asks for your vial and water first. What dose to take, and when to step up, belongs with a prescriber; the retatrutide dosage page lays out what the trials used.

How long a mixed vial lasts

No one has published how long retatrutide stays stable after it's mixed with bac water. What exists is a general FDA recommendation and the labels of approved drugs.

FDA recommends using any multi-dose vial of a sterile drug within 28 days of the first use, because the contamination risk rises after that. Its GLP-1 page says to throw the vial away at 28 days even if there's liquid left and even if the compounder's instructions say longer. Lilly's own Zepbound multi-dose vial, a ready-made tirzepatide liquid, carries a similar limit: throw it away 30 days after first use or after 4 weekly doses, whichever comes first. Labels for approved drugs differ, too: mixed Egrifta WR is kept at room temperature, never refrigerated, and thrown out after 7 days.

That 28-day line changes which vial makes sense. A 10 mg vial holds 5 doses of 2 mg, which on a weekly schedule runs right up to day 28. A 20 mg vial at 2 mg holds 10 weekly doses, so about half of it would still be in the vial when FDA says to throw it out.

Our read: Zepbound's multi-dose vial uses benzyl alcohol at 5.4 mg per 0.6 mL dose, which works out to 9 mg per mL, the same 0.9% as bac water, and Lilly still caps it at 4 doses. A home-mixed vial with no stability data has no better claim to a longer life.

For fridge temperatures, travel and what to do with a vial left out overnight, see retatrutide storage.

Mistakes that change the dose you get

FDA's 2024 alert on compounded semaglutide is the best record of what goes wrong with home-measured vials. That's semaglutide data, but the syringe is the same. Most reports described people drawing more than the prescribed dose from a multi-dose vial, and they took 5 to 20 times the intended amount. In one example people told to inject 5 units drew up 50. Prescribers made the same slip converting milligrams to units: one wrote 20 units instead of 2.

The ones to watch for:

• Confusing units, milliliters and milligrams. Write all three on the vial label.
• Mixing a new vial with a different water volume and not redoing the math.
• Using a syringe far bigger than the dose, which FDA flagged as a source of error.
• Reusing a needle or syringe. FDA says a new sterile one every time, because reuse can contaminate the vial.
• Adding a second peptide to the same vial or syringe. The bac water label warns about incompatible mixtures, and nothing has been tested with retatrutide.
• Freezing a mixed vial to make it last. Zepbound's label says not to use tirzepatide that's been frozen, and nothing published covers freezing retatrutide. A freeze-thaw thread on r/Retatrutide is one post, not a study.

For where to inject and at what angle, see how to inject retatrutide.

When to stop and get help

Stop using a vial that turns cloudy, changes color or grows particles, or that arrived warm; FDA advises against using any injectable GLP-1 drug shipped without proper cooling.

If you take insulin or a sulfonylurea, tell your doctor before starting any drug in this class. In a Zepbound trial in people with type 2 diabetes (tirzepatide data, not retatrutide), low blood sugar hit 10.3% of those also taking a sulfonylurea, against 2.1% of those who weren't. A red, hot, spreading patch around the injection site, pus, or a fever needs to be seen the same day.