Key takeaways
- Retatrutide is not FDA-approved. Lilly plans to file for approval in the first quarter of 2027.
- Units = dose (mg) × water (mL) × 100 ÷ vial (mg) on a U-100 syringe. A 10 mg vial with 2 mL makes 2 mg equal to 40 units.
- Trials stepped up every 4 weeks. Phase 3 started at 2 mg and moved through 4, 6 and 9 mg toward 12 mg.
- The 12 mg arm lost 24.2% at 48 weeks in phase 2 and 28.3% at 80 weeks in TRIUMPH-1.
- Water changes units, not doses. Recalculate every time you change the mix.
How to use the retatrutide calculator
The calculator does one job: it turns an amount of retatrutide in mg into a volume and a syringe reading. It needs four inputs, and it updates as you type.
- Peptide in the vial. Enter the total mg on the vial label. Retatrutide has no approved product, so there is no standard vial size. The buttons cover round sizes from 5 to 30 mg.
- Bacteriostatic water added. Enter the mL of diluent in the vial. If you have not mixed it yet, try a few volumes and watch how the units change.
- Dose per injection. Enter the amount in mg. Retatrutide amounts are written in mg, not mcg, so leave the unit on mg unless your source says otherwise.
- Syringe. All U-100 syringes read 100 units per mL. The barrel size sets capacity and how finely the marks are spaced.
- Check the result. Read the units and the mL. The calculator warns you if the amount is more than the vial holds, if it will not fit the syringe, or if the unit looks wrong.
What is retatrutide?
Retatrutide (development code LY3437943) is an investigational once-weekly injection from Eli Lilly. It is a single peptide attached to a fatty-acid chain, and it activates three hormone receptors: GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1) and glucagon. Researchers often call it a triple agonist. According to the phase 2 report in the New England Journal of Medicine, it is less potent than the body’s own hormones at the glucagon and GLP-1 receptors and more potent at the GIP receptor. Its half-life is about 6 days, which is what makes weekly dosing possible.
GLP-1 and GIP are gut hormones involved in appetite and insulin release. Glucagon is the third target. The NEJM authors explain the rationale: adding glucagon activity may further reduce energy intake, increase energy expenditure, or both. That extra target is the main difference from tirzepatide, which activates only GIP and GLP-1.
Is retatrutide FDA-approved?
No. Retatrutide is not approved by the FDA or any other regulator for any use. Lilly describes it as an investigational molecule that is legally available only to participants in its clinical trials. In its July 23, 2026 release, Lilly said it plans to submit a Biologics License Application to the FDA in the first quarter of 2027. Approval would come after that review, not before.
The FDA has also acted against retatrutide sold outside the trials. Its page on unapproved GLP-1 drugs, updated September 1, 2026, states that retatrutide cannot be used in compounding under federal law. It lists warning letters to telehealth companies, ingredient distributors and outsourcing facilities. It also says the FDA has warned companies selling retatrutide falsely labeled for research purposes or not for human consumption and sold directly to consumers with dosing instructions. One March 2026 warning letter called such products unapproved new drugs.
Retatrutide dosing chart from the clinical trials
People searching for a retatrutide dosing chart usually want to know what the trials did. The chart below shows the phase 2 trial arms exactly as published. It is a record of a study design, not a schedule to follow. In that trial, 338 adults with obesity were randomly assigned to one of six retatrutide arms or placebo for 48 weeks. Arms at 4 mg or higher began at 2 or 4 mg and stepped up every 4 weeks, for up to 12 weeks.
| Arm | People | Weekly steps | Top dose from wk | 48-wk change |
|---|---|---|---|---|
| 1 mg | 69 | 1 mg | 0 | −8.7% |
| 4 mg (start 2 mg) | 33 | 2 mg → 4 mg | 4 | −16.3% |
| 4 mg (start 4 mg) | 34 | 4 mg | 0 | −17.8% |
| 8 mg (start 2 mg) | 35 | 2 mg → 4 mg → 8 mg | 8 | −21.7% |
| 8 mg (start 4 mg) | 35 | 4 mg → 8 mg | 4 | −23.9% |
| 12 mg (start 2 mg) | 62 | 2 mg → 4 mg → 8 mg → 12 mg | 12 | −24.2% |
| Placebo | 70 | none | — | −2.1% |
Trial data, not dosing advice. The trial also found that starting at 2 mg rather than 4 mg partly reduced stomach side effects.
Phase 3 dose steps (TRIUMPH)
The phase 3 program used a gentler ramp. Lilly’s TRIUMPH-1 release says everyone assigned to retatrutide started at 2 mg once weekly and moved up one step every 4 weeks until reaching the assigned dose.
| Assigned dose | Weekly steps | Steps | Assigned dose from week |
|---|---|---|---|
| 4 mg | 2 mg → 4 mg | 2 | 4 |
| 9 mg | 2 mg → 4 mg → 6 mg → 9 mg | 4 | 12 |
| 12 mg | 2 mg → 4 mg → 6 mg → 9 mg → 12 mg | 5 | 16 |
What the retatrutide trials found
Phase 2 showed a clear dose response. By 48 weeks, weight loss ranged from −8.7% in the 1 mg arm to −24.2% in the 12 mg arm, against −2.1% with placebo. In the 12 mg arm, 83% of participants lost 15% or more of their body weight.
Lilly has since reported topline results from four phase 3 TRIUMPH trials. These are company press releases; full peer-reviewed papers may add detail. Figures below use Lilly’s efficacy estimand, which describes people who stayed on treatment.
| Trial | Population | Weeks | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|---|---|
| TRIUMPH-1 2,339 people · May 2026 | Obesity or overweight with a weight-related condition, no diabetes | 80 | −19.0% | −25.9% | −28.3% | −2.2% |
| TRIUMPH-2 1,152 people · July 2026 | Obesity or overweight with type 2 diabetes | 80 | −12.7% | −19.1% | −20.8% | −4.0% |
| TRIUMPH-3 1,949 people · July 2026 | Severe obesity with established cardiovascular disease | 80 | not tested | −21.6% | −22.6% | −3.2% |
| TRIUMPH-4 445 people · December 2025 | Obesity or overweight with knee osteoarthritis | 68 | not tested | −26.4% | −28.7% | −2.1% |
Sources: Lilly releases for TRIUMPH-4 (December 2025), TRIUMPH-1 (May 2026) and TRIUMPH-2 and -3 (July 2026).
In TRIUMPH-1, Lilly also reported a treatment-regimen result, which counts everyone randomized, of −25.0% at 12 mg. In an extension of participants who started with a BMI of 35 or higher, the 12 mg group averaged −30.3% at 104 weeks.
The retatrutide mg to units formula
Retatrutide math is the same as for any reconstituted peptide. The only twist is that amounts are usually in mg, so you can skip the mcg conversion.
All in one line: Units = dose (mg) × water (mL) × 100 ÷ vial (mg). Check: 2 × 2 × 100 ÷ 10 = 40 units.
| Term | Meaning | Unit |
|---|---|---|
| Vial | Total retatrutide in the vial | mg |
| Water | Bacteriostatic water added | mL |
| C | Concentration after mixing | mg/mL |
| Dose | Amount in one injection | mg |
| V | Volume to draw | mL |
| Units | U-100 syringe reading | units (100 per mL) |
Retatrutide mg to units chart
This chart answers one question: if your amount is X mg, how many U-100 units is it at a given concentration? Find your concentration across the top. The column header lists the vial and water mixes that produce it. Rows are round numbers for conversion, not suggested amounts.
| Amount | 2.5 mg/mL | 5 mg/mL | 10 mg/mL | 15 mg/mL |
|---|---|---|---|---|
| Mixes | 5 mg + 2 mL | 5 mg + 1 mL, 10 mg + 2 mL, 15 mg + 3 mL | 10 mg + 1 mL, 20 mg + 2 mL, 30 mg + 3 mL | 15 mg + 1 mL, 30 mg + 2 mL |
| 0.5 mg | 20 | 10 | 5 | 3.33 |
| 1 mg | 40 | 20 | 10 | 6.67 |
| 2 mg | 80 | 40 | 20 | 13.3 |
| 3 mg | over 100 | 60 | 30 | 20 |
| 4 mg | over 100 | 80 | 40 | 26.7 |
| 5 mg | over 100 | 100 | 50 | 33.3 |
| 6 mg | over 100 | over 100 | 60 | 40 |
| 8 mg | over 100 | over 100 | 80 | 53.3 |
| 9 mg | over 100 | over 100 | 90 | 60 |
| 10 mg | over 100 | over 100 | 100 | 66.7 |
| 12 mg | over 100 | over 100 | over 100 | 80 |
mL = units ÷ 100. “Over 100” means the amount is more than 1 mL at that concentration and will not fit a 1 mL U-100 syringe.
How much BAC water to add to a retatrutide vial
No water volume is correct in general. Each choice sets a concentration, and the concentration sets how many units each mg takes up. The table shows both for common vial sizes. To use it, multiply your amount in mg by the units-per-mg figure.
| Vial | 1 mL | 1.5 mL | 2 mL | 2.5 mL | 3 mL |
|---|---|---|---|---|---|
| 5 mg | 5 20 u/mg | 3.33 30 u/mg | 2.5 40 u/mg | 2 50 u/mg | 1.67 60 u/mg |
| 10 mg | 10 10 u/mg | 6.67 15 u/mg | 5 20 u/mg | 4 25 u/mg | 3.33 30 u/mg |
| 15 mg | 15 6.67 u/mg | 10 10 u/mg | 7.5 13.33 u/mg | 6 16.67 u/mg | 5 20 u/mg |
| 20 mg | 20 5 u/mg | 13.33 7.5 u/mg | 10 10 u/mg | 8 12.5 u/mg | 6.67 15 u/mg |
| 30 mg | 30 3.33 u/mg | 20 5 u/mg | 15 6.67 u/mg | 12 8.33 u/mg | 10 10 u/mg |
Top: mg/mL. Bottom: U-100 units per 1 mg. Example: 10 mg in 2 mL is 5 mg/mL and 20 units per mg, so 2 mg is 40 units.
Three rules keep the numbers manageable. More water makes each amount a larger, easier-to-read volume. Less water keeps large amounts inside one syringe. And whatever you choose, write the volume on the vial. The BAC water calculator solves for the water that puts an amount on a whole-unit mark.
Worked examples
Example 1: 10 mg vial, 2 mL water, 2 mg
Concentration is 10 ÷ 2 = 5 mg/mL. Volume is 2 ÷ 5 = 0.4 mL, which is 40 units on a U-100 syringe. The vial holds 5 of these amounts.
Example 2: 20 mg vial, 2 mL water, 4 mg
Concentration is 20 ÷ 2 = 10 mg/mL. Volume is 4 ÷ 10 = 0.4 mL, which is 40 units on a U-100 syringe. The vial holds 5 of these amounts.
Example 3: 15 mg vial, 1.5 mL water, 6 mg
Concentration is 15 ÷ 1.5 = 10 mg/mL. Volume is 6 ÷ 10 = 0.6 mL, which is 60 units on a U-100 syringe. The vial holds 2.5 of these amounts.
Example 4: 30 mg vial, 3 mL water, 12 mg
Concentration is 30 ÷ 3 = 10 mg/mL. Volume is 12 ÷ 10 = 1.2 mL, which is 120 units on a U-100 syringe. The vial holds 2.5 of these amounts. That is more than a 1 mL syringe holds, so the calculator shows a capacity warning. Less water gives a stronger mix: the same 30 mg vial with 2 mL is 15 mg/mL, which brings 12 mg down to 80 units.
To confirm how many weeks a vial covers at a steady amount, use the doses per vial calculator. To convert any mg or mL figure straight to units, use the mg to units calculator.
Retatrutide vs tirzepatide vs semaglutide
All three are once-weekly injections, but they activate different receptors. The table compares each drug’s targets and the headline result from its pivotal obesity trial at the highest dose studied.
| Drug | Receptors activated | Status | Pivotal trial | Highest dose | Weight change (placebo) |
|---|---|---|---|---|---|
| Retatrutide | GIP, GLP-1, glucagon | Investigational | TRIUMPH-1 (80 weeks) | 12 mg | −28.3% (−2.2%) |
| Tirzepatide | GIP, GLP-1 | FDA-approved | SURMOUNT-1 (72 weeks) | 15 mg | −20.9% (−3.1%) |
| Semaglutide | GLP-1 | FDA-approved | STEP 1 (68 weeks) | 2.4 mg | −14.9% (−2.4%) |
Sources: Lilly TRIUMPH-1 release; SURMOUNT-1 (NEJM 2022); STEP 1 (NEJM 2021). These trials were not head to head. Populations, durations and statistical methods differ, so the numbers are not directly comparable.
Tirzepatide and semaglutide have FDA labels with fixed dose schedules. If you use either, the tirzepatide calculator and semaglutide calculator show the labeled steps alongside the same unit math.
Side effects seen in the retatrutide trials
Safety data come from trial reports and company releases, not from an FDA label. Three themes recur.
- Stomach and bowel effects. In phase 2, nausea, diarrhea, vomiting and constipation were the most common adverse events. They were dose-related, mostly mild to moderate, happened mainly while the dose was being raised, and were partly reduced by starting at 2 mg instead of 4 mg. In TRIUMPH-1, nausea affected 42.4% at 12 mg versus 14.8% with placebo.
- Heart rate. In phase 2, heart rate rose with dose, peaked at 24 weeks and then declined at 36 and 48 weeks. The authors described the increases as similar to those reported with GLP-1 drugs.
- Skin sensation. Phase 2 reported skin sensitivity or hyperesthesia in 7% on retatrutide versus 1% on placebo. Phase 3 releases report dysesthesia, an unusual or unpleasant skin sensation, in up to 12.5% at 12 mg in TRIUMPH-1 and 20.9% at 12 mg in TRIUMPH-4, versus under 1% with placebo.
| Trial | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| TRIUMPH-1 | 4.1% | 6.9% | 11.3% | 4.9% |
| TRIUMPH-2 | 3.8% | 11.6% | 7.7% | 4.9% |
| TRIUMPH-3 | — | 9.8% | 13.5% | 4.8% |
| TRIUMPH-4 | — | 12.2% | 18.2% | 4.0% |
In phase 2, 6% to 16% of retatrutide participants stopped because of adverse events, versus none on placebo.
Storage
There is no FDA-approved retatrutide label, so there are no official storage instructions to quote. General principles for peptides still apply: follow whatever the product labeling says, keep freeze-dried powder cold, dry and away from light, refrigerate after mixing unless told otherwise, and never freeze a mixed vial unless the labeling allows it. Label every vial with the date mixed and the water volume. The peptide reconstitution calculator covers mixing technique and beyond-use dates in more detail.
Common mistakes with retatrutide math
The calculator’s warnings map to the errors that cause the biggest dosing mistakes with injectable peptides.
- Entering mg as mcg. 2 mg is 2,000 mcg. If the unit is set wrong, the answer is off by a factor of 1,000.
- Asking for more than the vial holds. 12 mg cannot come from a 10 mg vial. The calculator flags any amount larger than the whole vial.
- Overfilling the syringe. At low concentrations, large amounts exceed 100 units. Check the capacity warning before you draw.
- Reusing old unit counts after a new mix. “40 units” means 2 mg at 5 mg/mL but 4 mg at 10 mg/mL.
- Using a U-40 syringe. Each unit on a U-40 syringe is 2.5 times larger than a U-100 unit.
- Treating trial arms as a plan. The trial steps describe what researchers tested under medical supervision. They are not a schedule for anyone else.
Key terms
- Triple agonist
- A drug that activates three receptors. Retatrutide activates the GIP, GLP-1 and glucagon receptors.
- GIP
- Glucose-dependent insulinotropic polypeptide, a gut hormone that boosts insulin release after meals.
- GLP-1
- Glucagon-like peptide-1, a gut hormone that slows stomach emptying and reduces appetite.
- Dose escalation
- Starting at a low dose and raising it in steps, used in trials to reduce side effects.
- Efficacy estimand
- A trial analysis that estimates the effect in people who kept taking the drug as intended.
- BLA
- Biologics License Application, the filing a company submits to ask the FDA for approval.
- Dysesthesia
- An abnormal skin sensation, such as tingling or burning, without an obvious cause.
Frequently asked questions
Is retatrutide FDA-approved?
No. Retatrutide is an investigational drug from Eli Lilly. Lilly says it is legally available only to participants in its clinical trials, and it plans to submit a Biologics License Application to the FDA in the first quarter of 2027. The FDA has warned sellers marketing retatrutide as a research chemical and states that it cannot be used in compounding.
How many units is 2 mg of retatrutide?
It depends on the water in the vial. A 10 mg vial mixed with 2 mL is 5 mg/mL, so 2 mg is 0.4 mL, or 40 units on a U-100 syringe. With 1 mL of water it is 20 units. The mg to units calculator converts any amount.
What doses were used in the retatrutide trials?
The phase 2 NEJM trial tested 1, 4, 8 and 12 mg once weekly, with some arms starting at 2 or 4 mg and stepping up every 4 weeks. The phase 3 TRIUMPH trials tested 4, 9 and 12 mg, starting at 2 mg with 4-week steps. These are trial arms, not a dosing guide.
How much bacteriostatic water should I add to a 10 mg retatrutide vial?
No volume is standard, so recalculate for whatever you use. 1 mL gives 10 mg/mL, where 1 mg is 10 units. 2 mL gives 5 mg/mL (20 units per mg). 3 mL gives about 3.33 mg/mL (30 units per mg). The BAC water calculator works backward from a target unit count.
What is the half-life of retatrutide?
About 6 days, according to the phase 2 trial report in the New England Journal of Medicine. That long half-life is why the phase 2 and phase 3 trials gave it by injection once a week. A long half-life also means the drug takes weeks, not days, to clear after the last dose.
How much weight did people lose on retatrutide?
In the 48-week phase 2 trial, the 12 mg group lost an average of 24.2% of body weight, against 2.1% with placebo. In the 80-week TRIUMPH-1 trial, Lilly reported 28.3% at 12 mg against 2.2% with placebo. Results varied by population and were smaller in people with type 2 diabetes.
What are the side effects of retatrutide?
In the trials, the most common were gastrointestinal: nausea, diarrhea, vomiting and constipation, mostly mild to moderate and most frequent while the dose was being raised. Heart rate rose in a dose-dependent way in phase 2. Phase 3 trials also reported dysesthesia, an abnormal skin sensation, more often than with placebo.
How is retatrutide different from tirzepatide and semaglutide?
Semaglutide activates one receptor (GLP-1). Tirzepatide activates two (GIP and GLP-1). Retatrutide activates three: GIP, GLP-1 and glucagon. Semaglutide and tirzepatide are FDA-approved and have labeled dose schedules, while retatrutide is still investigational. For label-based unit math, see the tirzepatide calculator and semaglutide calculator.
Is retatrutide sold online the same as the trial drug?
There is no way to know. No retatrutide product is approved, so nothing sold outside Lilly’s trials has been checked by the FDA for identity, purity or sterility. The FDA has sent warning letters to companies selling retatrutide labeled for research purposes or not for human consumption.
How many doses are in a retatrutide vial?
Divide the mg in the vial by the mg per injection. A 10 mg vial holds five 2 mg amounts, whatever volume of water you add. Water changes the units per injection, not the number of injections. The doses per vial calculator adds dates and beyond-use limits.
Sources
We check every formula and figure on this page against primary sources. See our editorial policy for how we review content.
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial (Jastreboff et al.)
- Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1)
- Lilly’s triple agonist, retatrutide, successful in two additional Phase 3 obesity trials (TRIUMPH-2 and TRIUMPH-3)
- FDA’s concerns with unapproved GLP-1 drugs used for weight loss
- Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)
- Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)
Reviewed by the PeptideConvert Editorial Team
Last reviewed . PeptideConvert tools do arithmetic only. They do not recommend a dose, and nothing on this site is medical advice. Always follow the label and your prescriber. Read the full medical disclaimer.