Retatrutide Dosage Calculator: Units and Reconstitution

Q: How many units is 2 mg of retatrutide?

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

Q: How many units is 4 mg of retatrutide?

A 4 mg dose is 40 units from a 10 mg/mL solution, 80 units from a 5 mg/mL solution, and about 27 units from a 15 mg/mL solution. Doses above 100 units exceed a 1 mL syringe and need a more concentrated mix.

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

There is no single right answer; the water volume sets the concentration. Pick a volume that keeps your dose between about 10 and 100 units on a U-100 syringe. For a 10 mg vial, 1 mL of water works well across most of the titration range.

Q: What is the retatrutide dosing schedule?

Retatrutide has no FDA-approved schedule. In the Phase 2 obesity trial, the 12 mg group escalated 2 mg weekly for weeks 1-4, then 4 mg, then 8 mg, then 12 mg, about four weeks per step. This is a trial regimen for context, not medical advice.

Q: What is the starting dose of retatrutide?

In clinical trials the starting dose was 2 mg once weekly for the first four weeks. Starting at 2 mg rather than 4 mg reduced gastrointestinal side effects without compromising weight loss.

Q: What syringe do I need for retatrutide?

A standard U-100 insulin syringe (100 units = 1 mL). Smaller 0.5 mL or 0.3 mL barrels give finer markings for small draws. Do not use a U-40 veterinary syringe, which is a different scale and gives the wrong dose.

Q: How should I store retatrutide after reconstitution?

Store reconstituted retatrutide refrigerated at 2-8 C (36-46 F) and use within about four weeks. Never freeze it, keep it out of light, and discard if cloudy or discolored.

Q: Does retatrutide need to be reconstituted?

Retatrutide supplied in Eli Lilly's clinical trials comes pre-filled and does not need reconstitution. Reconstitution only applies to lyophilized research-grade powder. Retatrutide is investigational and cannot be legally purchased, prescribed, or compounded outside trials.

Q: Is retatrutide FDA approved?

No. Retatrutide is an investigational drug from Eli Lilly, not approved by the FDA, currently in Phase 3 (TRIUMPH) trials. Published references state it is available only to trial participants and cannot be legally purchased, prescribed, or compounded.

This is the most accurate Retatrutide Dosage Calculator and Retatrutide Reconstitution Calculator online. Enter your vial strength, bacteriostatic water, and dose. You will get the exact U-100 syringe units. We have added one-tap presets for the full investigational titration ladder. Use the Toggle button to switch to a second mode that converts a known concentration (mg/mL) straight to units.

Choose your calculation mode:

Reconstitute a vial: your retatrutide is dry powder (lyophilized). Enter the vial strength (mg) and the bacteriostatic water you add, and the calculator finds the concentration and your units.

Syringe Size

What is the total volume of your insulin syringe?

Concentration

Concentration printed on your vial label (mg/mL).

Enter concentration manually:

mg/mL

Vial Strength

Total mg of retatrutide in the vial.

Enter vial quantity manually:

Bacteriostatic Water

How much water are you adding to the vial?

Enter water amount manually:

Dose

How much retatrutide do you want per dose?

Enter dose manually:

Your Result

Set your options to see the result.

Retatrutide Dose

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Draw To

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Concentration

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Doses Per Vial

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Quick Presets — Retatrutide Titration Doses (Investigational)

Tap a titration dose from the Phase 2 trial ladder to load it. Presets set your dose only; your vial + water stays as-is. Retatrutide is investigational — these are trial doses, not an approved regimen.

Not medical advice — for education only. This Retatrutide Dosage Calculator performs a mathematical conversion only and assumes a standard U-100 insulin syringe (100 units = 1 mL). Retatrutide is an investigational drug that is not approved by the FDA and, according to published drug references, is available only through Eli Lilly’s clinical trials — it cannot be legally purchased, prescribed, or compounded. This tool does not endorse obtaining or using retatrutide. It illustrates the dosing math only. Always consult a licensed healthcare professional.

Important: Retatrutide is an investigational drug that has not been approved by the FDA. According to published drug references, it is available only to participants in Eli Lilly’s clinical trials and cannot be legally purchased, prescribed, or compounded. This page is educational and explains the dosing math reported in published trials. It does not recommend obtaining or using retatrutide. Always consult a licensed healthcare professional.

How the Retatrutide Dosage Calculator Works

The Retatrutide Dosage Calculator above converts a retatrutide dose in milligrams into the exact number of units to draw on a U-100 insulin syringe. Because retatrutide from research suppliers is almost always a lyophilized (freeze-dried) powder, the calculator runs primarily as a retatrutide reconstitution calculator: you enter the vial strength in mg and the bacteriostatic water you add, and it finds your concentration and units. A second mode lets you enter a known concentration (mg/mL) directly. Whichever mode you use, the output is the same — the precise units to draw for your dose.

The math behind retatrutide dosing is the same two-step calculation every insulin-syringe conversion uses:

Step 1 — Concentration (mg/mL) = Vial strength (mg) ÷ Bacteriostatic water (mL)
Step 2 — Units = (Dose in mg ÷ Concentration in mg/mL) × 100
Based on the U-100 insulin syringe standard, where 100 units = 1 mL.

For example, a 10 mg vial reconstituted with 2 mL of bacteriostatic water gives a concentration of 5 mg/mL. A 2 mg dose is then (2 ÷ 5) × 100 = 40 units. Change the water volume and the units change with it: the same 10 mg vial with only 1 mL of water becomes 10 mg/mL, and that same 2 mg dose is now just 20 units. This is why you must recalculate every time your vial size or water volume changes — copying someone else’s unit count only works if their reconstitution is identical to yours.

Retatrutide Reconstitution: Step by Step

Reconstitution is the process of turning the dry retatrutide powder into an injectable liquid by adding bacteriostatic water. Using the retatrutide reconstitution calculator above alongside these steps gives you the exact volume to draw:

Let the vial reach room temperature. Wipe the rubber stopper of both the retatrutide vial and the bacteriostatic water vial with a fresh alcohol swab.
Draw your chosen volume of bacteriostatic water into a syringe. Insert the needle at an angle and let the water run slowly down the inner glass wall of the vial — do not spray it directly onto the powder.
Swirl gently to dissolve. Never shake, as agitation can damage the peptide. The solution should turn clear; discard it if it stays cloudy or has particles.
Enter your vial strength, the water volume you used, and your dose into the calculator to get the exact units to draw on a U-100 syringe.
Store the reconstituted vial refrigerated at 2–8°C and use it within about four weeks. Never freeze it.

Choosing your water volume is a balance: more water makes the solution more dilute, so the same dose fills more of the syringe and is easier to measure precisely; less water concentrates it, so the draw is smaller. A practical target is a volume that keeps your dose between roughly 10 and 100 units, which is the easy-to-read range on a U-100 syringe.

Retatrutide Dose Chart: mg to Units

This retatrutide dosage chart shows how many U-100 units to draw for each investigational dose level across common reconstitution setups. Find your vial-and-water combination across the top, your dose down the left, and read off the units. For a fuller reference across every vial size, see our dedicated retatrutide dosage chart.

Dose	5 mg + 1 mL (5 mg/mL)	10 mg + 2 mL (5 mg/mL)	10 mg + 1 mL (10 mg/mL)	15 mg + 1 mL (15 mg/mL)
2 mg	40	40	20	13
4 mg	80	80	40	27
6 mg	over 100*	over 100*	60	40
8 mg	over 100*	over 100*	80	53
12 mg	over 100*	over 100*	over 100*	80

*Over 100 units exceeds a 1 mL U-100 syringe. Use less water (a higher concentration) or a larger vial so the draw stays under 100 units. Values are rounded; use the calculator for exact figures.

Retatrutide Dosing: The Investigational Titration Ladder

Retatrutide has no FDA-approved dosing schedule because it is investigational. What is published is the dose-escalation regimen used in the Phase 2 obesity trial (Jastreboff et al., New England Journal of Medicine, 2023). In that trial, the 12 mg group reached its target dose through gradual escalation, starting at 2 mg and increasing roughly every four weeks. Escalating slowly is what makes retatrutide dosing tolerable: the drug activates three hormone receptors at once, and a gradual ramp gives the body time to adjust, reducing the gastrointestinal side effects that are the most common reason people stop.

Weeks	Weekly Dose	Phase
Weeks 1–4	2 mg	Starting dose
Weeks 5–8	4 mg	First step-up
Weeks 9–12	8 mg	Second step-up
Weeks 13+	12 mg	Highest dose studied

This 2 → 4 → 8 → 12 mg pattern reflects the 12 mg target arm of the Phase 2 trial. The trial also tested 1 mg, 4 mg, and 8 mg target arms. Some sources present a smoother ladder (for example 2 → 4 → 6 → 9 → 12 mg) attributed to the ongoing Phase 3 TRIUMPH program; because the exact Phase 3 per-week schedule has not been fully published, the calculator’s presets follow the documented Phase 2 doses. These are trial doses for context only, not a recommended or approved regimen.

How Much Bacteriostatic Water Should You Use?

There is no single correct water volume — it sets your concentration, and the best concentration depends on the doses you plan to draw. The goal is to keep every dose in an easy-to-measure range on a U-100 syringe (about 10 to 100 units). For the low end of the titration ladder, more dilute mixes read more precisely; as doses climb toward 8–12 mg, a more concentrated mix (less water, or a larger vial) keeps the draw from exceeding a single syringe. The calculator’s auto-fill feature can suggest a water volume for you: leave the water field blank and it will compute the volume that makes your dose fill the selected syringe.

Quick Answers: How Much BAC Water for Retatrutide

There is no single “correct” amount of bacteriostatic (BAC) water — the volume you add sets the concentration, and the best concentration is the one that keeps your dose in an easy-to-read range on a U-100 syringe (roughly 10–100 units). Below are practical starting points for each common vial size. Enter your own numbers in the calculator above to confirm before drawing.

How much BAC water for 5 mg retatrutide?

For a 5 mg vial, adding 1 mL of bacteriostatic water gives a concentration of 5 mg/mL, so a 2 mg dose is 40 units. This keeps the low titration doses easy to measure. If you want a smaller, more concentrated draw, 0.5 mL of water gives 10 mg/mL (a 2 mg dose is then 20 units). Avoid going much more dilute than 1 mL, since larger doses would exceed a 1 mL syringe.

How much BAC water for 10 mg retatrutide?

For a 10 mg vial, 1 mL of bacteriostatic water is the most versatile choice: it gives 10 mg/mL, so a 2 mg dose is 20 units and the mix stays under a full syringe all the way up to a 9 mg dose. If you prefer a larger, easier-to-read draw at low doses, 2 mL of water gives 5 mg/mL (a 2 mg dose becomes 40 units), though doses of 6 mg and above then exceed a 1 mL syringe.

How much BAC water for 20 mg retatrutide?

For a 20 mg vial, 2 mL of bacteriostatic water gives 10 mg/mL, so a 2 mg dose is 20 units and even a 9 mg dose stays under a full syringe (90 units). Using 1 mL instead gives a concentrated 20 mg/mL — good for high doses (a 12 mg dose is 60 units) but the small low-dose draws (a 2 mg dose is just 10 units) are harder to measure precisely.

How much BAC water for 30 mg retatrutide?

For a 30 mg vial, 3 mL of bacteriostatic water gives 10 mg/mL, which keeps every titration dose in an easy range (a 2 mg dose is 20 units, a 12 mg dose is 120 units and would need splitting or a smaller water volume). For the highest doses, 2 mL gives 15 mg/mL so a 12 mg dose is 80 units on a single syringe. Larger vials like this suit people already at higher maintenance doses.

These are practical starting points for measuring accuracy, not medical dosing advice. Retatrutide is investigational and not FDA-approved. Always confirm your reconstitution and dose with a qualified professional.

What the Trials Showed

Retatrutide produced the largest weight reductions reported for any anti-obesity medication in trials to date. In the Phase 2 trial, adults with obesity lost a mean of 24.2% of body weight at 48 weeks on the 12 mg dose, with the 8 mg dose reaching about 22.8%. Later data cited from the ongoing program has pointed to roughly 28.7% at the highest dose over a longer 68-week period. For comparison, tirzepatide reached about 22.5% and semaglutide about 15% in their respective obesity trials. Retatrutide also produced striking reductions in liver fat — over 80% relative reduction at the 8 and 12 mg doses in a substudy of participants with fatty liver disease. Its half-life is about six days, which supports once-weekly dosing. These are averages from supervised clinical trials; individual results vary, and the drug remains investigational.

Retatrutide vs. Tirzepatide vs. Semaglutide

	Retatrutide	Tirzepatide	Semaglutide
Receptors	GIP + GLP-1 + glucagon (triple)	GIP + GLP-1 (dual)	GLP-1 (single)
Mean weight loss (trials)	~24% (up to ~28.7%)	~22.5%	~15%
FDA status	Investigational (not approved)	Approved (Mounjaro/Zepbound)	Approved (Ozempic/Wegovy)
Half-life	~6 days	~5 days	~7 days

Retatrutide Dosage Calculator: Frequently Asked Questions

How many units is 2 mg of retatrutide?

It depends entirely on your reconstitution. With a 10 mg vial and 1 mL of 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 — enter your exact numbers in the calculator above.

How many units is 4 mg of retatrutide?

A 4 mg dose is 40 units from a 10 mg/mL solution (for example a 10 mg vial with 1 mL water), 80 units from a 5 mg/mL solution, and about 27 units from a 15 mg/mL solution. Doses that come out above 100 units exceed a 1 mL syringe, so a more concentrated mix is needed.

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 is to pick a volume that keeps your dose between about 10 and 100 units (0.1–1 mL) so it is easy to read on a U-100 syringe. For a 10 mg vial, 1 mL of water works well across most of the titration range. Leave the water field blank in the calculator and it will suggest a volume.

What is the retatrutide dosing schedule?

Retatrutide has no FDA-approved schedule because it is investigational. In the Phase 2 obesity trial, the 12 mg group escalated gradually: 2 mg weekly for weeks 1–4, then 4 mg, then 8 mg, then 12 mg, with roughly four weeks at each step. Everyone started at 2 mg. This gradual titration reduces gastrointestinal side effects. It is a trial regimen for context, not medical advice.

What is the starting dose of retatrutide?

In the clinical trials, the starting dose was 2 mg once weekly for the first four weeks. Phase 2 data showed that starting at 2 mg rather than 4 mg significantly reduced gastrointestinal side effects without compromising long-term weight loss, which is why 2 mg is the standard trial starting point before escalation.

What syringe do I need for retatrutide?

The unit numbers here assume a standard U-100 insulin syringe (100 units = 1 mL). A 0.5 mL (50-unit) or 0.3 mL (30-unit) barrel gives finer markings for small draws; a 1 mL (100-unit) barrel covers larger draws. All U-100 syringes take the same number of units for the same dose. Do not use a U-40 veterinary syringe — it is a different scale and will give the wrong dose.

How should I store retatrutide after reconstitution?

Once reconstituted, store retatrutide refrigerated at 2–8°C (36–46°F) and use it within about four weeks. Never freeze it, and keep it out of direct light. Discard the solution if it becomes cloudy or discolored. Before reconstitution, the lyophilized powder is also kept refrigerated.

Does retatrutide need to be reconstituted?

The retatrutide supplied in Eli Lilly’s clinical trials comes pre-filled and ready to inject — it does not require reconstitution. Reconstitution only applies to lyophilized research-grade powder from outside the trials. Because retatrutide is investigational and not approved, published references note it cannot be legally purchased, prescribed, or compounded outside of clinical trials.

How much weight can you lose on retatrutide?

In the Phase 2 obesity trial, adults lost a mean of 24.2% of body weight at 48 weeks on the 12 mg dose, and about 22.8% on 8 mg. Longer follow-up data cited from the ongoing program has pointed to roughly 28.7% at the highest dose. These are trial averages with diet and activity support; individual results vary, and retatrutide is not yet approved.

Is retatrutide FDA approved?

No. Retatrutide is an investigational drug developed by Eli Lilly and is not approved by the FDA or any regulator. It is currently in Phase 3 (TRIUMPH) trials. According to published drug references, it is available only to clinical-trial participants and cannot be legally purchased, prescribed, or compounded. Any use outside a trial is unregulated and carries real risk.

What is retatrutide and how does it work?

Retatrutide (development code LY3437943) is a once-weekly triple hormone receptor agonist that activates the GIP, GLP-1, and glucagon receptors at the same time — the first “triple agonist” of its kind. The GLP-1 and GIP actions reduce appetite and improve blood sugar handling, while the added glucagon action increases energy expenditure. This triple mechanism is thought to explain its unusually large weight-loss effect in trials.

What are the side effects of retatrutide?

In trials the most common side effects were gastrointestinal — nausea, diarrhea, vomiting, and constipation — which were dose-related, mostly mild to moderate, and most common during dose escalation. A dose-dependent increase in heart rate was also observed, peaking around 24 weeks. Because retatrutide is investigational, its full long-term safety profile is still being studied. Discuss any medication decision with a licensed clinician.

Related Tools & Charts

Pair this calculator with the matching reference table: look up retatrutide units by dose and vial in the full chart, which lays out every common vial-and-water setup at a glance. If you are comparing the newer triple agonist with the approved GLP-1 options, you can also convert a tirzepatide dose to syringe units or calculate semaglutide syringe units with the same two-mode approach.

For the underlying reconstitution math on any compound, start from the main peptide reconstitution calculator, or browse every free dosage calculator in one place and the full dosage chart library. To understand the science behind these numbers, read our peptide guides and research.

Sources & References

Every dosing figure and trial result on this page traces to a primary source below. Retatrutide is investigational; always rely on your prescriber and published clinical evidence, not secondary tools, for medical decisions.

Peer-Reviewed Studies

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(6):514-526 (PubMed) — the landmark Phase 2 obesity trial establishing retatrutide’s dose-dependent weight loss (up to 24.2% at 48 weeks) and the 2→4→8→12 mg escalation.
Full text at the New England Journal of Medicine (DOI: 10.1056/NEJMoa2301972) — the complete published trial, including the dose-escalation protocol and safety data.
Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for MASLD: a randomized phase 2a trial. Nat Med. 2024 (PMC) — the liver-fat substudy confirming the ~6-day half-life and >80% liver-fat reduction at higher doses.

Manufacturer (Eli Lilly)

Eli Lilly: What to Know About Retatrutide — the developer’s official overview, confirming retatrutide is investigational and available only through Lilly’s clinical trials.
Eli Lilly: Phase 2 Retatrutide Results Announcement — Lilly’s summary of the NEJM Phase 2 data (up to 24.2% mean weight reduction at 48 weeks).

Clinical Trials & Regulatory

ClinicalTrials.gov: Phase 2 Retatrutide Obesity Trial (NCT04881760) — the official trial record, including the exact dose-escalation arms (2→4→8→12 mg).
Drugs.com: Retatrutide — Uses, Dosing, Side Effects — consumer drug reference confirming investigational status and that retatrutide cannot be legally purchased, prescribed, or compounded outside clinical trials.

General Reference

Wikipedia: Retatrutide — background on the molecule (LY3437943), its triple GIP/GLP-1/glucagon mechanism, development history, and trial results.
Wikipedia: Bacteriostatic Water — reference on the diluent used to reconstitute lyophilized peptides.
Wikipedia: Insulin Syringe (U-100 scale) — background on the U-100 unit standard (100 units = 1 mL) that this calculator uses.

Investigational drug notice: Retatrutide is not FDA-approved and is available only through Eli Lilly’s clinical trials. This page is educational and does not recommend obtaining or using retatrutide. Always consult a licensed healthcare professional before making any medical decision.