How does the retatrutide calculator work? dose to units in plain steps

What retatrutide is (and why "dose" is unsettled)

Retatrutide (development code LY3437943) is a single peptide that activates three receptors at once: the GIP, GLP-1 and glucagon receptors. The discovery and proof-of-concept pharmacology was published by Coskun and colleagues in Cell Metabolism in 2022, describing balanced glucagon and GLP-1 activity with stronger GIP activity and once-weekly dosing in early human studies. Because it engages glucagon as well, it is sometimes called a "triple G" agonist rather than a GLP-1 drug like semaglutide or a dual agonist like tirzepatide.

The honest caveat: retatrutide has only reached phase 2, with phase 3 trials ongoing, and it is not approved by the FDA or any major regulator. The phase 2 obesity trial reported by Jastreboff in the New England Journal of Medicine (2023) tested weekly doses up to 12 mg over 48 weeks; the phase 2 type 2 diabetes trial reported by Rosenstock in The Lancet (2023) tested a similar range. Those are research doses titrated under trial supervision — there is no consumer label, no standard vial, and no established self-administration schedule. This guide explains only the arithmetic of converting a number you already have into a syringe volume.

How this is calculated

The maths is the same volume-and-ratio arithmetic used for any reconstituted peptide. Three quantities matter: the dose (mg of drug you want), the concentration (mg per mL after you add water), and the volume (mL you draw). They relate by one identity:

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

Retatrutide ships as a lyophilised (freeze-dried) powder, so the vial itself has no concentration until you add bacteriostatic water. Concentration is set by you: a 10 mg vial reconstituted with 1 mL is 10 mg/mL, but the same vial with 2 mL is 5 mg/mL. That single choice changes every unit number on the page, which is why copying someone else's "units" without matching their water volume is unsafe.

To read the volume on an insulin syringe, convert mL to U-100 units: a U-100 syringe is marked so that 100 units = 1 mL, meaning units = mL × 100. Combine the two steps and the whole conversion is:

units = (dose mg ÷ concentration mg/mL) × 100

No rounding is applied for you here — if a result lands between marks (say 7.5 units), you read the nearest practical line on your syringe. A 0.3 mL syringe spreads small draws across more visible marks than a 1 mL barrel, which helps when volumes are tiny.

Retatrutide dose to units chart

The table below shows the U-100 unit mark for common research dose points at three concentrations you might create by reconstituting a 10 mg vial with 1 mL (10 mg/mL), 2 mL (5 mg/mL) or 2.5 mL (4 mg/mL). Read it as arithmetic, not advice.

*Values above 100 units exceed a standard 1 mL U-100 syringe and would need either a more concentrated mix or more than one draw. The table makes the core lesson visible: at a fixed dose, a more dilute mix means more units; at a fixed concentration, a bigger dose means more units.

The concentration ladder, drawn

Worked examples

Each block below is plain arithmetic you can check by hand. They use the trial dose range purely as reference points — none is a recommendation.

Common mistakes

The biggest error is treating retatrutide units like a fixed recipe. Because the powder has no built-in concentration, your water volume sets everything — 20 units and 40 units can be the identical 2 mg dose from the identical vial, differing only in how much bacteriostatic water was added. Always pair a unit number with its mg/mL.

The second is unit confusion: mixing milligrams with micrograms drops or adds a factor of 1000, and reading a U-100 mark as if it were "mg" treats a volume line as a dose. The third is ignoring that these are trial doses — escalating quickly toward the 12 mg ceiling seen in studies, outside the slow titration and monitoring those trials used, is not something this maths page endorses.

So, how does the retatrutide calculator work?

The retatrutide calculator works by dividing your dose in mg by your vial concentration in mg/mL to get the draw volume in mL, then multiplying by 100 to give the mark on a U-100 insulin syringe — the full formula is units = (dose mg divided by concentration mg/mL) multiplied by 100. Because retatrutide ships as a powder, you set the concentration yourself when you add bacteriostatic water, which means your water volume is part of the calculation. Plug your own numbers into the free retatrutide dose to units calculator to get the syringe mark instantly.

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