Free retatrutide reconstitution calculator. Enter vial size (5-15 mg), BAC water volume, and weekly dose to get concentration, syringe units, and doses per vial. Includes the Phase 2/3 trial titration protocol (1-12 mg weekly), triple-agonist dosing reference, and comparison with tirzepatide. Verify retatrutide quality with independent lab test data on Peptigrity.
A 10 mg vial of Retatrutide reconstituted with 2 mL of bacteriostatic water gives a concentration of 5.0 mg/mL, or 50 mcg per unit on a U-100 syringe. For a 2 mg dose, draw the syringe to 40.0 units (0.40 mL). At that dose the vial provides about 5 doses.
Defaults (10 mg vial, 2 mL, 2 mg) carried over unchanged from this calculator's live defaults (2 September 2026). Arithmetic only, not a recommendation.
Draw the syringe up to
That's one 2 mg dose. Add 2 mL of water to your 10 mg vial first.
| Step | Dose | Draw on a U-100 | Doses per vial |
|---|---|---|---|
| Tier 1 (start) | 2 mg | 40 units | 5 |
| Tier 2 | 4 mg | 80 units | 2 |
| Tier 3 | 8 mg | Exceeds syringe — split the dose or use less water | 1 |
| Phase 3 dose arm | 9 mg | Exceeds syringe — split the dose or use less water | 1 |
| Tier 4 (max) | 12 mg | Exceeds syringe — split the dose or use less water | — |
Tap any row to load that dose into the calculator above.
The Phase 2 trial (Jastreboff et al., NEJM 2023, n=338) established a 4-week step-up escalation from 2 mg to 12 mg. Participants who started at higher doses or escalated too quickly experienced nearly double the rate of gastrointestinal side effects. The ongoing TRIUMPH Phase 3 programme administers 4 mg, 9 mg and 12 mg weekly as dose arms under clinical supervision; no Phase 3 results have been published.
| Titration Tier | Weekly Dose | Weeks | At 6 mg/mL | At 10 mg/mL | At 20 mg/mL |
|---|---|---|---|---|---|
| Tier 1 (starting) | 2 mg | Weeks 1-4 | ~33 units | 20 units | 10 units |
| Tier 2 | 4 mg | Weeks 5-8 | ~67 units | 40 units | 20 units |
| Tier 3 | 8 mg | Weeks 9-12 | Exceeds 100u | 80 units | 40 units |
| Tier 4 (Phase 2 max) | 12 mg | Week 13+ | Exceeds 100u | Exceeds 100u | 60 units |
| Phase 3 dose arm | 9 mg | Ongoing — no results published | Exceeds 100u | 90 units | 45 units |
At 20 mg/mL (20 mg vial + 1 mL, or 30 mg vial + 1.5 mL), the entire titration schedule through 12 mg fits within 60 units - the cleanest measurement. The calculator flags syringe capacity warnings automatically.
Peptigrity does not recommend a dose; these are the doses studied in the phase 2 trial (Jastreboff et al., “Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial,” New England Journal of Medicine 2023;389(6):514–526, PMID 37366315), which randomised 338 participants for 48 weeks, double-blind and placebo-controlled. The table below lists every source of a retatrutide dose figure in circulation with its evidence level; as of 11 August 2026 PubMed contains no phase 3 retatrutide results paper, and retatrutide is not approved anywhere we could verify.
| Route | Amount | Frequency | Duration | Evidence level |
|---|---|---|---|---|
| Subcutaneous | 1 mg | Once weekly | 48 weeks | Human RCT — phase 2 arm, n=338 |
| Subcutaneous | 4 mg | Once weekly | 48 weeks | Human RCT — phase 2 arm, n=338 |
| Subcutaneous | 8 mg | Once weekly | 48 weeks | Human RCT — phase 2 arm, n=338 |
| Subcutaneous | 12 mg | Once weekly | 48 weeks | Human RCT — phase 2 arm, n=338 |
| Any escalation ladder in 1–2 mg increments | Chosen by the user | Chosen by the user | Chosen by the user | Convention — no trial tested a ladder |
| Any amount attributed to phase 3 | — | — | — | No phase 3 results exist |
| Any regulator-approved dose | — | — | — | None exists anywhere |
The results by arm, as published for the 24- and 48-week readouts, are below. At least 15% weight loss was achieved by 60–83% of participants across doses, against 2% on placebo.
| Arm | 24 weeks | 48 weeks |
|---|---|---|
| 1 mg | −7.2% | −8.7% |
| 4 mg | — | −17.1% |
| 8 mg | — | −22.8% |
| 12 mg | −17.5% | −24.2% |
| Placebo | −1.6% | −2.1% |
Read the evidence-level column rather than the amount column. The four trial rows describe randomised groups that were each given a fixed amount and compared against placebo. They do not describe a route from one to the next, and a trial that assigns people to 1 mg or 12 mg is not a trial of climbing from 1 mg to 12 mg. The schedule table above presents a step-up from 2 mg to 12 mg as what the Phase 2 trial ran; our phase 2 fact base records four separate arms and no tested ladder. Both are printed here so neither is resolved silently. Flagged for editorial resolution, September 2026. Phase 3 is set out trial by trial in the TRIUMPH programme.
The sites are describable; the schedule for moving between them is not. Retatrutide has no label, so the site facts below come from approved labels for other peptides. What is measured is the consequence of concentrating injections: injection site reactions occurred in 25% of patients on tesamorelin's approved label, with trial tables recording 17% against 6% on placebo across 543 tesamorelin and 263 placebo patients over 26 weeks. The table below gives each site's provenance.
| Site | Named on an approved peptide label? | Provenance | Note |
|---|---|---|---|
| Abdomen | Yes — bremelanotide's label names it | Approved label (another compound) | Broadest area, easiest to inspect, away from the navel |
| Thigh | Yes — bremelanotide's label names it | Approved label (another compound) | Front and outer aspect; alternates naturally with the abdomen |
| Upper arm | No | Convention, not label | Harder to self-administer and to inspect |
| Upper buttock | No | Convention, not label | Not self-visible |
| Any site with a lump, bruise or reaction | — | — | Not usable. Skip it and record why |
| A rotation interval in weeks | — | Not sourced | No trial has compared rotation schemes for any peptide in this fact base |
Two absences belong in that table rather than in a footnote. No trial has compared rotation schemes, so every “return to a site after N weeks” figure in circulation is convention rather than measurement. And no approved peptide label in this fact base specifies a needle gauge for a self-administered research vial, so Peptigrity does not publish one. What is measurable is the reaction rate itself, and bremelanotide's label records 13.2% against 8.4%. Tissue injected repeatedly is tissue injured repeatedly, and a 25% reaction rate under supervised conditions with correct technique is a floor rather than a ceiling. General technique is in how to inject peptides, and the route argument in subcutaneous versus intramuscular injection. Anything about your own tissue, symptoms or medication is a clinician's question.
Step 1 - Choose BAC Water Volume. For the full titration through 12 mg in a single draw, target 20 mg/mL (e.g. 20 mg vial + 1 mL BAC water). At 10 mg/mL, doses up to 10 mg fit within 100 units. The BAC water calculator recommends volumes based on your dose and syringe.
Step 2 - Reconstitute. Inject BAC water slowly against the inside glass wall. Retatrutide dissolves within 1-3 minutes of gentle swirling. Solution should be clear and colourless. See reconstituting peptides step by step.
Step 3 - Store. Refrigerate at 2-8°C. Stable for approximately 28 days. See how to store peptides.
The storage step above gives approximately 28 days refrigerated at 2–8 °C. Our injection-technique fact base does not support that number for retatrutide: no approved label sets an in-use period for this compound and no published stability data in our fact base covers it, so a “discard after N days” figure attached to a research vial is borrowed from a compound that had a label. Treat 28 days as a convention, not a measurement. Flagged for editorial resolution, September 2026.
Concentration is peptide mass divided by diluent volume: a 20 mg vial reconstituted with 2 mL of bacteriostatic water gives 10 mg/mL, or 10,000 mcg/mL. No label specifies a diluent volume for retatrutide, because no label exists — the only regulator-backed peptide reconstitution instruction in our fact base belongs to tesamorelin, a different compound entirely. At 10 mg/mL, 1 mg is 10 units and 12 mg is 120 units — more than a 1 mL barrel holds. Retatrutide's distinctive arithmetic problem sits at the other end: a large vial in a small volume pushes small amounts below the resolution of any syringe. The worked example below draws the same 1 mg amount from a 60 mg vial at two diluent volumes.
| Step | 60 mg in 2 mL | 60 mg in 6 mL |
|---|---|---|
| Concentration | 30 mg/mL | 10 mg/mL |
| Volume for 1 mg | 0.033 mL | 0.1 mL |
| U-100 units | 3.3 units — poor resolution | 10 units |
The fix in the left-hand column is more diluent, not a steadier hand, and it has to be chosen before anything is mixed. That is an example of a calculation, not a recommendation about an amount. The reconstitution calculator performs the same division, and the general form of the arithmetic is in how to calculate peptide doses.
| Factor | Retatrutide | Tirzepatide | Semaglutide |
|---|---|---|---|
| Receptor targets | Triple: GLP-1 + GIP + Glucagon | Dual: GIP + GLP-1 | GLP-1 only |
| Starting dose | 2 mg weekly | 2.5 mg weekly | 0.25 mg weekly |
| Maximum dose | 12 mg weekly | 15 mg weekly | 2.4 mg weekly |
| Phase 2 weight loss (48 wk) | 24.2% at 12 mg | 22.5% at 15 mg | 15.8% at 2.4 mg |
| Common vial sizes | 5, 10, 12, 20, 30 mg | 5, 10, 15, 30, 60 mg | 2, 3, 5, 10 mg |
| Regulatory status | Phase 3 (not yet approved) | FDA-approved | FDA-approved (Ozempic/Wegovy) |
Retatrutide's glucagon receptor activity adds thermogenesis and hepatic fat reduction that dual-agonists lack - but it also carries a different side effect profile. For compound-specific calculators, see the tirzepatide calculator and semaglutide calculator.
| Vial Size | At 2 mg/wk | At 4 mg/wk | At 8 mg/wk | At 12 mg/wk |
|---|---|---|---|---|
| 5 mg | 2.5 weeks | 1.25 weeks | - | - |
| 10 mg | 5 weeks | 2.5 weeks | 1.25 weeks | - |
| 12 mg | 6 weeks | 3 weeks | 1.5 weeks | 1 week |
| 20 mg | 10 weeks | 5 weeks | 2.5 weeks | ~1.7 weeks |
| 30 mg | 15 weeks | 7.5 weeks | 3.75 weeks | 2.5 weeks |
Reconstituted retatrutide is conventionally given approximately 28 days refrigerated, though no approved label or published stability study sets an in-use period for this compound (see the storage note above). For price comparisons, use the cost-per-dose calculator.
Quantity variance on retatrutide runs −4% to +22.5% against label across 1,150 independent lab tests on this platform (verified August 2026), with most results within ±5%. Unlike tirzepatide, where the recorded variance is one-directional and always over, retatrutide's runs both ways — so a vial can hold less than the label claims as easily as more. The table below shows what each end of that recorded range delivers for an intended amount.
| Intended amount | At −4% | At +22.5% |
|---|---|---|
| 1 mg | 0.96 mg | 1.23 mg |
| 2 mg | 1.92 mg | 2.45 mg |
| 4 mg | 3.84 mg | 4.90 mg |
| 8 mg | 7.68 mg | 9.80 mg |
| 12 mg | 11.52 mg | 14.70 mg |
An intended 12 mg — the highest amount any randomised trial has administered — delivers 14.7 mg from a vial at the top of the recorded range, which is an amount no trial has tested at all. And the underfill direction is not benign either: it produces an unknown exposure that looks like a known one. Purity does not answer this question; a vial can sit inside retatrutide's 99.52% to 99.98% purity band and still be 22.5% over on quantity — see why 10 mg isn't 10 mg.
Injecting into a lump, a bruise or a reactive patch belongs on that list too, and it is the one error visible while it is happening.
At 6 mg/mL (12 mg vial + 2 mL BAC water): ~33 units. At 10 mg/mL: 20 units. At 20 mg/mL: 10 units. Use the calculator above with your specific vial and BAC water volume for exact numbers.
Phase 2 protocol: 2 mg weekly for weeks 1-4, 4 mg for weeks 5-8, 8 mg for weeks 9-12, and 12 mg from week 13 onward. The ongoing TRIUMPH Phase 3 programme administers 4, 9 and 12 mg weekly as dose arms under clinical supervision; no Phase 3 results have been published.
2 mL produces 6 mg/mL - practical for starting doses but exceeds syringe capacity above 6 mg. 1 mL produces 12 mg/mL - covers doses up to 12 mg in 100 units. The BAC water calculator recommends volumes based on your dose and syringe.
Retatrutide is a triple-agonist targeting GLP-1, GIP, and glucagon receptors simultaneously. Tirzepatide is a dual-agonist (GIP + GLP-1 only). Retatrutide's glucagon receptor activity adds thermogenesis and hepatic fat reduction. In Phase 2 trials, 12 mg retatrutide achieved 24.2% weight loss at 48 weeks - the highest reported for any injectable.
It depends entirely on the concentration. At 10 mg/mL, 4 mg is 0.4 mL, which is 40 units on a U-100 syringe. At 30 mg/mL the same amount is 13.3 units. Any units figure quoted without a concentration cannot be used, and cannot be corrected without knowing the vial size and the diluent volume.
Abdomen and thigh are the sites named on an approved peptide label, bremelanotide's; upper arm and upper buttock are convention. On rotation frequency there is no evidence-based answer, because no trial has compared rotation schemes for any peptide in this fact base. What is measured is the consequence: 25% injection site reactions on tesamorelin's label under supervised conditions.