Investigational drug warning: retatrutide is not FDA-approved and has not been approved by any regulatory agency. Lilly states that people should not take products claiming to be retatrutide outside a Lilly-sponsored clinical trial. This page does not provide instructions for purchasing, reconstituting, preparing, or self-injecting unapproved retatrutide.
Retatrutide reconstitution & dose calculator
Retatrutide Dosage Calculator
Medically reviewed by Dr. Jaydeep Sanghani, MBBS, MDLast reviewed August 2026
Divide your target dose by the concentration in mg/mL. Concentration is vial mg divided by the bacteriostatic water you added in mL. A 10 mg vial with 2 mL of water gives 5 mg/mL, so a 2 mg dose is 0.40 mL — 40 units on a U-100 insulin syringe. The calculator below does all three steps for you.
Get your injection volume in mL and units, the Phase 2 weekly ladder, vial duration and a shareable schedule. Educational only, not medical advice.
Retatrutide Dosage Calculator
Enter your vial strength, the bacteriostatic water you plan to add and your target dose. Everything else is calculated instantly.
Vial strength (mg per vial)
How many milligrams of retatrutide are in one vial before you add any water. Check the label.
Bacteriostatic water added (mL)
The total volume of bacteriostatic or sterile water you draw into the vial. Common choices are 1 mL, 2 mL or 3 mL.
Desired dose per injection (mg)
The milligrams of retatrutide you want in each injection. Do not choose a dose without discussing it with a prescriber.
Injection frequency
How often you plan to inject. Retatrutide has a half-life of about 6 days and once weekly dosing was used in trials.
Syringe type
The syringe you will draw with. U-100 insulin syringes are the most common, 100 units per 1 mL.
Planned treatment length (weeks)
Used to project how much retatrutide the plan will consume and when your vials will run out.
Preferred injection day
Your regular injection day. This anchors the calendar and the next injection date.
Current weight (optional)
Optional. Used only for the weight tracking chart. Never used to recommend a dose.
Goal weight (optional)
Optional.
Draw this much
Units
40u
Volume
0.4mL
Concentration
5mg/mL
2 mg divided by 5 mg/mL equals 0.4 mL, and 1 mL is 100 units, so that is 40 units.
Educational only. Retatrutide is an investigational drug in clinical trials and is not FDA approved. Never dose without a licensed prescriber.
Your Results
Everything below is calculated from your inputs, in your browser.
Estimated drug activity
Vial usage
Estimated remaining medication in your current vial at the end of the plan. You will need approximately 3 vials in total.
Weekly dose table
The plan below assumes you keep the same dose the whole way. If your prescriber steps you up, recalculate at the new dose.
| Week | Dose | Volume (mL) | Units | Cumulative mg | Vial remaining | Date |
|---|---|---|---|---|---|---|
| 1 | 2 mg | 0.4 mL | 40 u | 2 mg | 8 mg | Mon, Sep 14 |
| 2 | 2 mg | 0.4 mL | 40 u | 4 mg | 6 mg | Mon, Sep 21 |
| 3 | 2 mg | 0.4 mL | 40 u | 6 mg | 4 mg | Mon, Sep 28 |
| 4 | 2 mg | 0.4 mL | 40 u | 8 mg | 2 mg | Mon, Oct 5 |
| 5 | 2 mg | 0.4 mL | 40 u | 10 mg | 0 mg | Mon, Oct 12 |
| 6 | 2 mg | 0.4 mL | 40 u | 12 mg | 8 mg | Mon, Oct 19 |
| 7 | 2 mg | 0.4 mL | 40 u | 14 mg | 6 mg | Mon, Oct 26 |
| 8 | 2 mg | 0.4 mL | 40 u | 16 mg | 4 mg | Mon, Nov 2 |
| 9 | 2 mg | 0.4 mL | 40 u | 18 mg | 2 mg | Mon, Nov 9 |
| 10 | 2 mg | 0.4 mL | 40 u | 20 mg | 0 mg | Mon, Nov 16 |
| 11 | 2 mg | 0.4 mL | 40 u | 22 mg | 8 mg | Mon, Nov 23 |
| 12 | 2 mg | 0.4 mL | 40 u | 24 mg | 6 mg | Mon, Nov 30 |
Injection calendar
12 injections scheduled. First on Mon, Sep 14 2026, last on Mon, Nov 30 2026.
Tool Information
September 2026
Dr. Jaydeep Sanghani
Meet Akabari
Dr. Jaydeep Sanghani
MBBS, MD, DNB(Anaesth.), PDCC(CCM), DrNB(CCM)
AIIMS Bhubaneswar · AIIMS Rishikesh
Critical care specialist and anesthesiologist with advanced training from AIIMS. Reviews health calculators at Calqulate to ensure medical accuracy and evidence-based standards.
30-second utility summary
This page explains the three mathematical relationships behind concentration, liquid volume, and U-100 volume markings, while keeping them separate from clinical dosing. Retatrutide remains an investigational drug. The formulas below are educational cross-checks for understanding published research math, not instructions for preparing or injecting products sold as retatrutide.
Retatrutide concentration math: the three equations
Concentration math has three separate steps: calculate concentration, calculate liquid volume from a known amount, and translate mL into U-100 volume markings. These equations are unit-conversion relationships only; they do not establish a safe dose or a safe preparation method for an investigational drug.
Step 1
Concentration
Concentration (mg/mL) = amount (mg) ÷ liquid volume (mL)
This states how many milligrams are present per millilitre.
Step 2
Volume from a known amount
Volume (mL) = amount (mg) ÷ concentration (mg/mL)
This is a general algebraic rearrangement, not a dosing recommendation.
Step 3
U-100 volume translation
U-100 marking = volume (mL) × 100
U-100 markings represent volume. They are not milligrams or micrograms.
Why this page does not provide retatrutide reconstitution recipes
A worked recipe such as “add X mL, then draw Y units” would turn a general equation into actionable preparation instructions for an unapproved drug. Because products sold outside authorized trials may have unknown identity, purity, concentration, or sterility, this page intentionally stops at the math relationships.
mg vs. mcg: the 1,000-fold metric error
One milligram equals 1,000 micrograms, so confusing mg with mcg creates a 1,000-fold unit error. Metric units should be checked before any arithmetic, especially when reviewing research labels, trial documents, or third-party peptide packaging.
| Milligrams | Micrograms |
|---|---|
| 0.5 mg | 500 mcg |
| 1 mg | 1,000 mcg |
| 2 mg | 2,000 mcg |
| 4 mg | 4,000 mcg |
| 8 mg | 8,000 mcg |
| 12 mg | 12,000 mcg |
What doses were studied in the 2023 Phase 2 obesity trial?
The NEJM Phase 2 obesity trial studied once-weekly target-dose groups of 1 mg, 4 mg, 8 mg, and 12 mg, with different starting-dose strategies in some higher-dose groups. Participants assigned to 4 mg or higher used protocol-defined escalation every 4 weeks for up to 12 weeks. These were controlled research regimens, not an approved community dosing ladder.
| Trial arm | Starting dose | Target dose | Trial escalation | Interpretation |
|---|---|---|---|---|
| 1 mg | 1 mg | 1 mg | No escalation to a higher target | Phase 2 obesity trial arm |
| 4 mg | 2 mg or 4 mg | 4 mg | Some participants started at 2 mg and escalated | Historical trial protocol, not a prescribing schedule |
| 8 mg | 2 mg or 4 mg | 8 mg | Gradual escalation every 4 weeks for up to 12 weeks | Historical trial protocol, not a prescribing schedule |
| 12 mg | 2 mg | 12 mg | Gradual escalation every 4 weeks for up to 12 weeks | Historical trial protocol, not a prescribing schedule |
Retatrutide Phase 3 status in 2026: TRIUMPH, not TRANSCEND
Lilly's Phase 3 retatrutide program is called TRIUMPH, and retatrutide remains investigational as of September 1, 2026. Lilly announced positive topline Phase 3 results from TRIUMPH-1 in May 2026 and from TRIUMPH-2 and TRIUMPH-3 in July 2026. The company has stated that it plans to submit a Biologics License Application to the FDA in Q1 2027.
TRIUMPH-1
Adults with obesity or overweight plus at least one weight-related comorbidity, without diabetes. Positive topline results announced May 2026.
TRIUMPH-2
Adults with obesity or overweight and type 2 diabetes. Positive topline results announced July 2026.
TRIUMPH-3
Adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes. Positive topline results announced July 2026.
Regulatory status
Lilly states that retatrutide has not been approved by any regulatory agency and warns against products claiming to be retatrutide outside Lilly-sponsored clinical trials.
Retatrutide half-life and steady-state build-up
Published Phase 2 data describe retatrutide as having an elimination half-life of approximately 6 days, supporting once-weekly dosing in clinical trials. Repeated exposure accumulates over several half-lives, so plasma concentrations would be expected to approach steady state over roughly 4 weeks or longer rather than after the first injection.
Retatrutide is a single peptide agonist at three receptor systems: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon receptors. This distinguishes it mechanistically from tirzepatide's dual GIP/GLP-1 agonism and semaglutide's GLP-1 agonism. For general elimination modeling, see the GLP-1 Half-Life Calculator.
What adverse events were reported in the Phase 2 obesity trial?
Gastrointestinal adverse events were the most common events reported with retatrutide in the Phase 2 obesity trial and were dose-related, with most described as mild to moderate. The trial also reported dose-dependent increases in heart rate that peaked at 24 weeks and declined afterward.
Gastrointestinal events were the most commonly reported adverse-event category.
The gastrointestinal event pattern was dose-related in the Phase 2 study.
Lower starting-dose strategies partially mitigated gastrointestinal events in the research protocol.
Dose-dependent heart-rate increases were observed and peaked around week 24.
Keep your prescribed GLP-1 history in one timeline
Calqulate Vitals is designed for tracking prescribed GLP-1 treatment history, weight trends, symptoms, nutrition and progress over time. Do not use it to create or follow a self-directed retatrutide protocol outside an authorized clinical trial.
- Prescribed injection and dose-change history
- Weight and symptom trends
- Medication timeline and reminders
- Doctor-ready progress reports (Premium)
Related calculators and trackers
Sources and references
This page is built from public clinical guidance and peer-reviewed research. Always confirm decisions with a licensed clinician.
Retatrutide research and safety FAQs
Frequently Asked Questions
Common questions and answers about this calculator.
Is retatrutide FDA-approved?
No. As of September 1, 2026, retatrutide remains investigational and has not been approved by the FDA or any other regulatory agency. Eli Lilly has announced positive Phase 3 topline results and has stated that it plans an FDA submission in the first quarter of 2027.
What is retatrutide?
Retatrutide is an investigational once-weekly peptide that activates GIP, GLP-1 and glucagon receptors. It is being studied for obesity and related metabolic conditions but is not an approved prescription medicine.
What doses were studied in the 2023 Phase 2 obesity trial?
The Phase 2 obesity trial studied once-weekly target-dose groups of 1 mg, 4 mg, 8 mg and 12 mg. Some higher-dose groups used 2 mg or 4 mg starting doses with gradual escalation every 4 weeks. These were research protocols, not approved dosing instructions.
What is the half-life of retatrutide?
Published Phase 2 data describe an elimination half-life of approximately 6 days, which supports once-weekly administration in clinical trials. Half-life does not provide instructions for self-dosing an investigational product.
How long does retatrutide take to approach steady state?
With an approximately 6-day half-life, repeated weekly exposure would be expected to approach pharmacokinetic steady state over several half-lives, roughly 4 weeks or more. Exact accumulation depends on the studied regimen and individual pharmacokinetics.
How do concentration calculations work?
The general laboratory relationship is concentration = amount of substance ÷ liquid volume, and volume = amount ÷ concentration. On this page, that relationship is presented for educational math verification only and should not be used to prepare or inject unapproved retatrutide products.
How much bacteriostatic water should I add to retatrutide?
This page does not provide reconstitution instructions for retatrutide. Retatrutide is investigational and products sold outside authorized clinical trials may have unknown identity, purity, strength or sterility. Do not choose a diluent volume from an online calculator.
Can I use an insulin syringe for retatrutide?
This page does not recommend a syringe or injection method for unapproved retatrutide. U-100 syringe markings represent volume, not milligrams, and using them safely requires a verified product, concentration and professional instructions.
What is the difference between mg and mcg?
One milligram equals 1,000 micrograms. Confusing mg and mcg creates a 1,000-fold unit error, which is why metric units should always be checked before any calculation.
What side effects were reported in the Phase 2 obesity trial?
The most common adverse events were gastrointestinal and were generally dose-related, with events described as mostly mild to moderate. The published trial also reported dose-dependent increases in heart rate that peaked at 24 weeks and later declined.
What is the status of the Phase 3 retatrutide program in 2026?
Lilly calls the Phase 3 program TRIUMPH. In 2026 it announced positive topline results from TRIUMPH-1, TRIUMPH-2 and TRIUMPH-3. Retatrutide remains investigational, and Lilly has said it plans an FDA submission in Q1 2027.
Medical and regulatory disclaimer: Retatrutide is an investigational drug and is not approved by the FDA or any other regulatory agency as of September 1, 2026. This page summarizes published research and general unit-conversion mathematics. It does not provide a retatrutide dose, reconstitution recipe, syringe instruction, sourcing guidance, or personalized treatment plan.
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