Retatrutide Calculator: Units & Reconstitution

Q: What syringe do I need for retatrutide?

The unit numbers on this page assume a U-100 insulin syringe (100 units = 1 mL), the standard for subcutaneous peptide injections. A 0.5 mL (50-unit) syringe offers finer markings for small draws; a 1 mL (100-unit) syringe covers larger draws. See How to Inject Retatrutide for technique.

This page is the working-tools companion to our Retatrutide Dosage & Dosing Guide. The guide covers the full titration schedules, weight loss by dose level, missed doses, and tapering — this page is for the math: an interactive calculator, syringe-unit conversion tables for every common reconstitution setup, and projected weight loss by starting weight.

Retatrutide is an investigational drug that has not been approved by the FDA. Pharmaceutical retatrutide in clinical trials comes pre-filled — reconstitution only applies to grey-market vials, which carry real risks. For what retatrutide is likely to cost and the legitimate ways to access it, see Retatrutide Cost & How to Get It.

Retatrutide Dose Calculator

Use the interactive calculator below to plan a dose escalation timeline with personalized calendar dates, or to calculate syringe units for your vial and water volume.

Dose Escalation Timeline

Enter your start date and target dose to see your personalized titration schedule with calendar dates.

Start date

Target dose

Weeks	Dose
1–4	2 mg
5–8	4 mg
9–12	6 mg
13–16	9 mg
17+	12 mg

Disclaimer: This calculator is for informational purposes only and does not constitute medical advice. Dosing schedules are based on the Phase 3 TRIUMPH clinical trial protocols. Always follow your healthcare provider's instructions.

Reconstitution Math: From Vial to Syringe Units

Lyophilized retatrutide is measured in milligrams, but insulin syringes are marked in U-100 units, where 100 units = 1 mL. Converting takes two steps:

Concentration = vial size (mg) ÷ bacteriostatic water added (mL)
Units to draw = dose (mg) ÷ concentration (mg/mL) × 100

Worked example: a 10 mg vial reconstituted with 1 mL of bacteriostatic water gives 10 mg/mL. A 2 mg dose is 2 ÷ 10 = 0.2 mL, which is 20 units on a U-100 insulin syringe.

Units Per Dose by Reconstitution Setup

U-100 syringe units for each titration dose level, across the common vial and water combinations:

Dose	5 mg + 1 mL	10 mg + 1 mL	10 mg + 2 mL	20 mg + 1 mL	20 mg + 2 mL
2 mg	40 units	20 units	40 units	10 units	20 units
4 mg	80 units	40 units	80 units	20 units	40 units
6 mg	over 100*	60 units	over 100*	30 units	60 units
9 mg	over 100*	90 units	over 100*	45 units	90 units
12 mg	over 100*	over 100*	over 100*	60 units	over 100*

* More than 100 units exceeds a full 1 mL U-100 syringe. For higher doses, use a more concentrated mix (less water per vial) or a larger vial so the draw stays under 1 mL — splitting a dose across two injections adds error and injection-site burden.

Concentration for each column: 5 mg + 1 mL = 5 mg/mL · 10 mg + 1 mL = 10 mg/mL · 10 mg + 2 mL = 5 mg/mL · 20 mg + 1 mL = 20 mg/mL · 20 mg + 2 mL = 10 mg/mL.

Doses follow the clinical-trial titration ladder (2 → 4 → 6 → 9 → 12 mg in 4-week steps). For the full week-by-week schedules per target dose, see the Phase 3 TRIUMPH titration schedule.

Projected Weight Loss by Starting Weight

Based on Phase 3 data (12 mg dose, 68 weeks, 28.7% mean weight loss):

Starting Weight	Projected Loss (~29%)	Projected Final Weight
200 lbs (91 kg)	~58 lbs	~142 lbs
225 lbs (102 kg)	~65 lbs	~160 lbs
250 lbs (113 kg)	~72 lbs	~178 lbs
275 lbs (125 kg)	~80 lbs	~195 lbs
300 lbs (136 kg)	~87 lbs	~213 lbs
350 lbs (159 kg)	~101 lbs	~249 lbs

These are averages based on the TRIUMPH-4 mean. Individual results vary — some lose more, some less. For weight loss broken down by dose level and trial, see weight loss by dose level.

When to Hold a Dose Increase

Escalation should only proceed if the current dose is well-tolerated. Consider staying at your current dose for an additional 2-4 weeks if you experience:

Persistent nausea or vomiting lasting more than 3 days
Rapid weight loss exceeding 3-4 lbs per week
Severe constipation or diarrhea
Signs of dehydration
Significant injection site reactions

The goal is to reach the maintenance dose gradually. Rushing escalation increases the risk and severity of side effects without improving long-term outcomes.

Full Dosing Guide

Everything beyond the calculators lives in the Dosage & Dosing Guide:

Phase 3 TRIUMPH titration schedules — week-by-week for 4, 9, and 12 mg targets
Weight loss by dose level — Phase 2, TRIUMPH-4, and T2D trial data
What to do if you miss a dose
How retatrutide dosing compares to tirzepatide and semaglutide
Stopping retatrutide and tapering

Frequently Asked Questions

How many units is 2 mg of retatrutide?

It depends entirely on your reconstitution. With a 10 mg vial + 1 mL bacteriostatic water (10 mg/mL), 2 mg is 20 units on a U-100 syringe. With 2 mL of water in the same vial (5 mg/mL), 2 mg is 40 units. Always recalculate when the vial size or water volume changes.

How much bacteriostatic water should I add to a retatrutide vial?

There is no single right answer — the water volume sets the concentration, and the right concentration depends on your dose. A practical rule: pick a volume that keeps your dose between 10 and 100 units (0.1-1 mL) so it is easy to measure accurately on a U-100 syringe. For a 10 mg vial, 1 mL of water works for every titration dose up to 9 mg.

What syringe do I need for retatrutide?

The unit numbers on this page assume a U-100 insulin syringe (100 units = 1 mL), the standard for subcutaneous peptide injections. A 0.5 mL (50-unit) syringe offers finer markings for small draws; a 1 mL (100-unit) syringe covers larger draws. See How to Inject Retatrutide for technique.

Can I start at a higher dose?

No. Clinical trials always begin at 2 mg and escalate gradually over 12-16 weeks. Starting at a higher dose dramatically increases the risk and severity of gastrointestinal side effects. The gradual approach allows your body to adjust.

Does pharmaceutical retatrutide need reconstitution?

No. Retatrutide supplied in Eli Lilly's clinical trials comes pre-filled and ready to inject. Reconstitution only applies to grey-market lyophilized vials, which are unregulated and carry contamination, dosing, and identity risks — see How to Reconstitute Retatrutide (and Why You Shouldn't).

Sources

Jastreboff, A.M., et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity. NEJM. DOI: 10.1056/NEJMoa2301972.
Eli Lilly. (2025). TRIUMPH-4 results. Press release.
Giblin, M.J., et al. (2026). Design of the TRIUMPH Phase 3 program. Diabetes, Obesity and Metabolism. PubMed.

Questions to ask your doctor

Given my health history, is a GLP-1 medication appropriate for me at all?
Which approved option (e.g. semaglutide, tirzepatide) best fits my goals?
What starting dose and titration pace would you use, and why?
What side effects should I watch for, and when should I call you?
How will we monitor whether it's working and when to adjust?

How we keep this honest

What this is: Educational information, not medical advice. It reports published research — it doesn’t recommend that you use, obtain, or supply anything.
Regulatory status: Retatrutide and similar peptides are investigational — not approved by the FDA or any regulator. Semaglutide and tirzepatide are prescription-only medicines, available only through a licensed prescriber.
Our standard: Every claim traces to a primary source. We label the strength of evidence and flag estimates as estimates — never as clinical fact.
No commercial ties: We don’t sell, supply, or link to suppliers of any medicine, and aren’t affiliated with any manufacturer.

Do not make decisions about your health without consulting a qualified healthcare provider. For trial enrolment, see ClinicalTrials.gov. More on how we review.

Sources