Retatrutide Units to mg (Syringe Chart for Every Mix)

Retatrutide units are marks on an insulin syringe, and they measure liquid, not drug. On a U-100 syringe, 100 units is 1 mL, so 20 units is always 0.2 mL, but how many milligrams that holds depends on how much water went into the vial: 20 units is 1 mg at 5 mg per mL, 2 mg at 10 mg per mL and 4 mg at 20 mg per mL. Every retatrutide trial dosed in milligrams, so a units number only means something next to the vial's strength.

Most charts online convert milligrams into units for one or two mixes. This page also runs it the other way, from the number on your syringe back to the dose, and covers the syringe mistakes that turn a correct chart into a wrong dose.

How units turn into milligrams

MedlinePlus, the National Library of Medicine's patient site, puts the scale plainly: standard insulin has 100 units in 1 mL, and "most insulin syringes are marked for giving you U-100 insulin." Those syringes keep the same scale whatever liquid you draw into them. One unit is 0.01 mL.

So two steps convert any draw:

1. Divide the units by 100 to get mL. 25 units is 0.25 mL.
2. Multiply the mL by the vial's strength in mg per mL. At 10 mg per mL, 0.25 mL holds 2.5 mg.

Going the other way, divide the dose in mg by the strength to get mL, then multiply by 100. A 2 mg dose at 5 mg per mL is 0.4 mL, or 40 units.

The strength is the one number you can't skip. It's the milligrams in the vial divided by the milliliters of water added: a 10 mg vial with 2 mL of bacteriostatic (bac) water makes 5 mg per mL. If you don't know it, no chart can tell you your dose. Our guide on how to reconstitute retatrutide covers the mixing itself, and the reconstitution calculator works out the strength from your vial and water.

The retatrutide units chart for common mixes

This is the reverse lookup: find the number of units on your syringe in the left column, then read across to your mix. Every cell is the arithmetic above.

Which vials make which strength (the 10 mg vial page has the week-by-week math for the most common size): 2.5 mg per mL is a 5 mg vial with 2 mL of water; 5 mg per mL is a 5 mg vial with 1 mL or a 10 mg vial with 2 mL; 10 mg per mL is a 10 mg vial with 1 mL or a 20 mg vial with 2 mL; 15 mg per mL is a 30 mg vial with 2 mL; 20 mg per mL is a 20 mg vial with 1 mL.

Read across any row. 20 units of retatrutide runs from 0.5 mg to 4 mg across this table, an eightfold spread. 40 units runs from 1 mg to 8 mg. Someone repeating "I take 20 units" on a forum is telling you almost nothing unless they also say how they mixed the vial.

How many units of retatrutide should you take?

Nobody can answer that in units, because no trial measured a dose that way. Lilly's TRIUMPH-1 trial, which randomized 2,339 adults, started everyone on retatrutide at 2 mg once a week and stepped up every 4 weeks toward 4, 9 or 12 mg. Our retatrutide dosage chart lays out the full ladder, and the retatrutide starting dose page covers the first step.

The doses people ask about most, in units:

• 1 mg: 20 units at 5 mg per mL, 10 units at 10 mg per mL, 5 units at 20 mg per mL.
• 2 mg: 40 units, 20 units or 10 units at those same three strengths.
• 4 mg: 80 units, 40 units or 20 units.

Is 10 units of retatrutide enough?

At 10 mg per mL, 10 units is 1 mg, half the Phase 3 starting dose. The 2023 Phase 2 obesity trial in The New England Journal of Medicine kept one group at 1 mg for the whole trial, and that group lost 8.7% of body weight on average over 48 weeks, against 2.1% on placebo.

At 5 mg per mL, the same 10 units is 0.5 mg. The 2023 Phase 2 diabetes trial in The Lancet had a 0.5 mg group, and it lost 3.19% over 36 weeks, barely more than the 3.00% on placebo.

Whether 1 mg is the right place to start, and when to step up, is a conversation for your doctor.

What size syringe for reta?

U-100 insulin syringes are sold in more than one barrel size, and the unit scale follows from the mL on the label. These are the ones you'll usually see, plus the one to avoid.

Pick the smallest syringe that holds your whole draw. FDA's July 2024 alert on compounded semaglutide said some patients "have been given syringes that are significantly larger than the prescribed volume," and counted that among the things that can confuse people measuring a dose. That's semaglutide, not retatrutide, but people drawing retatrutide from a vial use the same U-100 syringes. A 10-unit dose sits at the very bottom of a 1 mL barrel, where a small slip is a big share of the dose.

The spacing of the marks isn't the same on every syringe. MedlinePlus describes a standard 1 mL syringe with a mark for every unit; the syringe in our figure above marks every 2 units. Count the lines between two printed numbers on your own syringe before your first draw. Our injection guide covers the draw and the injection itself.

Strength matters here too. At 20 mg per mL, a 2 mg dose is only 10 units, and misreading it by one 2-unit mark changes the dose by 0.4 mg, or 20%. At 5 mg per mL, the same 2 mg is 40 units, and one 2-unit slip is 0.1 mg, or 5%.

Our read: a weaker mix makes the early, smaller doses easier to measure accurately, and a stronger one keeps the big doses inside one syringe. At 5 mg per mL, 12 mg would be 240 units, more than two full 1 mL syringes, so the right mix depends on which dose you're measuring.

The U-40 syringe trap

Not every insulin syringe is U-100. The FDA-approved label for Vetsulin, an insulin for dogs and cats, says it holds 40 units per mL and warns, in capitals, that using any syringe other than a U-40 syringe "will result in incorrect dosing." U-40 syringes exist for that insulin, so the words "insulin syringe" on a box don't tell you which scale you have.

On a U-40 syringe each unit is 0.025 mL, not 0.01 mL. Draw to the 20 mark on one and you have 0.5 mL, not 0.2 mL. At 10 mg per mL, that's 5 mg instead of 2 mg: 2.5 times the dose, from a syringe that looks almost the same. Check that the barrel or the box says U-100 before you use any units chart, including ours.

Units, mL and the reta pen question

Some searches ask in milliliters. The conversion is fixed on a U-100 syringe: 10 units is 0.1 mL, 20 units is 0.2 mL, 50 units is 0.5 mL. How many mL to inject depends on the dose and the strength, and it's the same division as before: mg divided by mg per mL. A 4 mg dose at 10 mg per mL is 0.4 mL.

Pens are a different story, because there's no approved one. ClinicalTrials.gov lists a Lilly study that compared 2 versions of retatrutide for different injection devices in 57 healthy people; it finished in February 2024 and, as of October 31, 2026, has no results posted.

Approved drugs like tirzepatide work the opposite way to a mixed vial. The Zepbound (tirzepatide) label lists single-dose pens that each hold 0.5 mL whatever the dose, and a KwikPen with 2.4 mL that gives four 0.6 mL doses. The strength of the liquid changes between pen doses; the volume doesn't, so there are no units to count. That's tirzepatide, not retatrutide.

Pens sold as retatrutide exist anyway. In October 2025 the UK's MHRA seized more than 2,000 unlicensed retatrutide and tirzepatide pens at a facility in Northampton. Victoria's health department, in its June 2026 alert on liver injury, listed products labeled Retatrutide, Reta, R-10 and R-20. Whatever those labels say about milligrams or milliliters is the seller's claim, not a checked number.

If you're weighing retatrutide for sale (see also whether retatrutide is legal), the units math on this page is only as good as the milligrams on the vial, and a batch-specific third-party test that states the amount per vial is the one way to check that number. In a September 2026 advisory, Australia's TGA said it had tested a vial sold as retatrutide after a serious adverse event report and found no retatrutide at all, but undeclared semaglutide at about 8 times the level in approved semaglutide products.

Unit mix-ups that change the dose

FDA's 2024 alert on compounded semaglutide spells out what went wrong when people measured a drug like this in units at home. In the measurement-error reports, people took 5 to 20 times the intended dose of semaglutide from a multi-dose vial. Some had been told to draw 5 units, which is 0.05 mL, and drew 50 units instead. Prescribers slipped too. One meant to prescribe 0.25 mg, which was 5 units at that strength, and wrote 25 units. Another wrote 20 units where 2 units was meant, giving 3 patients 10 times the intended dose. Some of those people ended up in hospital.

Retatrutide vials leave room for the same slips, because there's no standard vial size or water volume:

• Using someone else's units number with a different water volume. Their 20 units and your 20 units can be different doses.
• Getting the mg-to-units conversion wrong, as in the 25 units written for 0.25 mg.
• Changing the water volume with a new vial and keeping the old units number.
• Assuming the vial holds what the label says.

Write the strength in mg per mL and the mixing date on the vial as soon as it's mixed (our storage guide covers how long a mixed vial lasts), and keep the dose written in mg and in units side by side. Our retatrutide calculator does the division for any vial and water amount.

As of October 2026, no approved retatrutide product exists. Lilly's October 2026 FAQ says of retatrutide: "It has not been reviewed or approved by the FDA or any regulatory agency in the world, and no one can legally sell it for human use." It also warns that illicit products can hold too much or too little active ingredient, or the wrong one. Lilly last said, on September 29, 2026, that it plans to submit retatrutide to the FDA in the first quarter of 2027 as a Biologics License Application (BLA). On October 2, 2026, the FDA decided that retatrutide is a drug, not a biological product, so an application would need to be filed under section 505 of the Federal Food, Drug, and Cosmetic Act. Lilly's appeal on that question is pending in the Seventh Circuit, and we found no ruling as of October 31, 2026. If a product is approved, its label will set the doses and the device.