How much BAC water for 20mg retatrutide — your complete reconstitution calculator
How much BAC water for 20mg retatrutide?
Calculator + Complete Guide
Get the exact bacteriostatic water volume for your retatrutide vial — with an interactive calculator, full concentration table, step-by-step mixing instructions, and storage guidelines.
The short answer
Add 2 mL of BAC water to a 20mg retatrutide vial. This gives you a clean concentration of 10 mg/mL, where every 0.1 mL (10 units on a U-100 syringe) equals exactly 1 mg. Use the calculator below to adjust for any concentration or dose you need.
What is retatrutide?
Retatrutide (development code: LY3437943) is an investigational peptide developed by Eli Lilly. It acts as a triple agonist — simultaneously targeting GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon receptors. Researchers study it for its potential role in metabolic research, making it one of the most studied next-generation peptide compounds.
Retatrutide is supplied as a lyophilized (freeze-dried) powder in sterile vials, most commonly in 5 mg, 10 mg, and 20 mg sizes. Before use in research, you must reconstitute it — dissolve the powder in a sterile liquid, most often bacteriostatic water (BAC water).
Retatrutide is an investigational compound and is not approved by the FDA or any regulatory authority for human therapeutic use. This guide is strictly for educational and research purposes.
Why use BAC water for retatrutide?
Bacteriostatic water (BAC water) is sterile water for injection that contains 0.9% benzyl alcohol as a preservative. It is the standard diluent for peptide reconstitution because it prevents microbial contamination across multiple draws from the same vial.
| Diluent | Preservative | Multi-use safe? | Shelf life after reconstitution |
|---|---|---|---|
| BAC water ✅ | 0.9% benzyl alcohol | Yes — up to 28 days | ~28 days (refrigerated) |
| Sterile water for injection | None | Single use only | Use within hours |
| Bacteriostatic saline | 0.9% benzyl alcohol | Yes — up to 28 days | ~28 days (refrigerated) |
| Normal saline (plain) | None | Single use only | Use within hours |
Plain sterile water contains no preservative. Once you puncture the vial seal and draw from it, airborne bacteria can enter. For multi-dose research vials, BAC water is strongly preferred to maintain sterility across the full 28-day use window.
BAC water calculator for retatrutide
Select your vial size and desired concentration. The calculator instantly shows you how much BAC water to add, your resulting concentration, and exactly how much to draw per dose.
Retatrutide BAC Water Calculator
Adjust values to get your exact reconstitution numbers
20mg retatrutide reconstitution table
This table covers the five most common BAC water volumes for a 20 mg vial. It shows the resulting concentration, plus the exact draw volume and U-100 syringe units you need for a 1 mg dose.
| BAC water added | Concentration | Draw for 1 mg dose | U-100 units | Best for |
|---|---|---|---|---|
| 1 mL | 20 mg/mL | 0.05 mL | 5 units | Very small injection volumes |
| 2 mL ⭐ Recommended | 10 mg/mL | 0.10 mL | 10 units | Most protocols — easy math |
| 4 mL | 5 mg/mL | 0.20 mL | 20 units | Lower concentration preference |
| 10 mL | 2 mg/mL | 0.50 mL | 50 units | Very dilute — smaller doses |
| 20 mL | 1 mg/mL | 1.00 mL | 100 units | Maximum dilution — micro-dosing |
At 10 mg/mL, the dose math is clean — every 0.1 mL equals exactly 1 mg. This reduces calculation errors during research. The draw volume stays small enough to be comfortable while remaining easy to measure accurately on a U-100 syringe.
How to calculate your draw volume
Once you know your concentration, use this simple formula to calculate every draw volume. You never need to guess — every dose has an exact number.
U-100 syringe conversion
A U-100 insulin syringe holds 100 units per mL. To convert your draw volume in mL to syringe units, multiply by 100.
How to reconstitute retatrutide with BAC water
Proper reconstitution technique preserves peptide integrity and prevents contamination. Follow these seven steps exactly.
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1Gather your suppliesYou need: your retatrutide vial, a vial of BAC water, two sterile syringes (one for drawing BAC water, one for injecting), a sterile needle (18–23g for reconstitution), alcohol swabs, and a clean surface. Check the expiry dates on all supplies before you start.
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2Clean both vial tops with alcohol swabsWipe the rubber stopper of both the retatrutide vial and the BAC water vial with a fresh alcohol swab. Allow each to air-dry for 30 seconds. Skipping this step is the most common source of vial contamination.⏱ Wait 30 seconds after swabbing — do not blow dry or wipe again.
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3Draw your calculated volume of BAC waterInsert the needle into the BAC water vial and draw back the plunger to pull in your required volume. For a 20 mg vial at 10 mg/mL, draw 2.00 mL. Confirm the measurement against the syringe markings before proceeding.
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4Inject BAC water slowly along the vial wallPush the needle into the retatrutide vial through the rubber stopper. Angle the needle so that the stream of BAC water runs gently down the inner glass wall — never aim the stream directly at the lyophilized powder cake. Inject slowly over 10–15 seconds.🔑 Side-wall injection prevents foaming and protects the peptide structure.
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5Gently swirl — never shakeRemove the needle and slowly roll the vial between your palms or gently swirl in a circular motion. Continue until the powder dissolves completely. Never shake the vial. Shaking introduces air bubbles and can denature the peptide, reducing its potency.
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6Inspect the solutionHold the vial up to a light source. The reconstituted solution should be clear and colorless, with no visible particles or cloudiness. If the solution appears cloudy, discolored, or contains floating matter, discard the vial and do not use it.
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7Label and store immediatelyWrite directly on the vial label or attach a sticker with: the concentration (e.g., 10 mg/mL), the reconstitution date, and your initials. Place the vial in your refrigerator (2–8°C) within five minutes of reconstitution. Never leave it at room temperature.📅 Mark the date clearly — reconstituted BAC water peptides expire in 28 days.
Do not inject BAC water directly onto the peptide powder. Do not shake the vial. Do not use the same needle for the BAC water vial and the retatrutide vial without changing it. Each of these actions damages the peptide or risks contamination.
How to store reconstituted retatrutide
Storage conditions directly affect how long your reconstituted retatrutide remains effective. Use the table below to plan your research timeline.
| Storage condition | Temperature | Estimated stability | Notes |
|---|---|---|---|
| 🧊 Refrigerator | 2–8°C (36–46°F) | Up to 28 days | Preferred for active use |
| ❄️ Freezer | −20°C (−4°F) | Several months | Avoid repeated freeze-thaw cycles |
| 🌡️ Room temperature | 20–25°C (68–77°F) | Not recommended | Degrades within hours |
| 📦 Lyophilized (unreconstituted) | 2–8°C or −20°C | 12–24 months | Check manufacturer COA for exact date |
If you freeze your reconstituted retatrutide, thaw it only once. Repeated freezing and thawing breaks peptide bonds and degrades potency rapidly. If your research spans more than 28 days, reconstitute a second vial rather than extending a single reconstituted batch.
Supplies checklist for retatrutide reconstitution
Collect everything before you start. Missing one item mid-process forces you to abandon sterile technique.
| Item | Specification | Purpose |
|---|---|---|
| Retatrutide vial | Lyophilized, sealed | The peptide you are reconstituting |
| Bacteriostatic water | 0.9% benzyl alcohol, sterile | Diluent — the liquid you add |
| Syringe for reconstitution | 1–3 mL sterile syringe | Drawing and injecting BAC water |
| Syringe for dosing | U-100 insulin syringe (29–31g) | Drawing and administering doses |
| Needle for reconstitution | 18–23g, sterile | Puncturing vial septa |
| Alcohol swabs | 70% isopropyl alcohol | Sterilizing vial tops |
| Vial labels or marker | Waterproof ink | Labeling concentration and date |
Frequently asked questions
These are the most common questions researchers ask about reconstituting retatrutide with BAC water.
Add 2 mL of bacteriostatic water to a 20 mg retatrutide vial. This gives you a concentration of 10 mg/mL, making each 0.1 mL equal to 1 mg. This is the most widely used starting concentration in research because the math stays simple and draw volumes stay small. Use the calculator above to adjust if your protocol calls for a different concentration.
Adding 2 mL of BAC water to a 20 mg vial gives you a concentration of exactly 10 mg per mL. At this concentration: 0.10 mL = 1 mg, 0.15 mL = 1.5 mg, 0.20 mL = 2 mg, and 0.25 mL = 2.5 mg. On a standard U-100 insulin syringe, 0.10 mL reads as 10 units.
Technically yes, but it is not recommended for multi-use vials. Sterile water for injection contains no preservative, so once you puncture the vial and draw from it the first time, microbial contamination risk increases with every subsequent draw. Sterile water is safe only for single-dose, immediate-use reconstitution. For any research protocol that draws from the same vial more than once, use BAC water.
When reconstituted with BAC water and stored at 2–8°C (36–46°F), retatrutide remains stable for approximately 28 days. Always mark the reconstitution date on the vial label and discard after 28 days, even if solution remains. If you need longer storage, keep the reconstituted vial in the freezer at −20°C — but do not re-freeze after thawing.
The peptide itself is not harmed. Adding more BAC water than intended simply lowers the concentration. Recalculate your actual concentration using the formula: Concentration = Total mg ÷ Actual mL added. Then recalculate your draw volume using the new concentration. For example, if you added 3 mL instead of 2 mL to a 20 mg vial, your concentration is 20 ÷ 3 = 6.67 mg/mL — and a 1 mg dose requires 0.15 mL instead of 0.10 mL.
A very faint straw or pale yellow color is sometimes normal and can result from the peptide’s amino acid composition or trace amounts of excipients in the lyophilized cake. However, dark yellow, orange, or brown coloration indicates degradation and the vial should be discarded. If in doubt, compare to a reference image from your supplier’s certificate of analysis (COA). A good solution is always clear — it must never be cloudy or contain floating particles.
Yes. Bacteriostatic saline (0.9% sodium chloride with benzyl alcohol) is a valid alternative to BAC water for peptide reconstitution. Both contain benzyl alcohol as a preservative and provide the same multi-use stability. Some researchers prefer saline because it more closely mirrors physiological conditions. Confirm with your specific research protocol before substituting.
Use a U-100 insulin syringe (1 mL total volume, 100 units per mL) with a 29–31 gauge needle for drawing and administering research doses. This syringe provides the finest graduation (each unit = 0.01 mL), giving you the accuracy needed for small dose volumes. A 29g needle minimizes discomfort during subcutaneous administration in animal models. Avoid large-volume syringes (3 mL, 5 mL) for dosing — they are harder to read accurately at the small volumes peptide research requires.
This article is for educational and research purposes only. Retatrutide (LY3437943) is an investigational compound. It is not approved by the FDA, EMA, or any other regulatory authority for human therapeutic use. Nothing in this guide constitutes medical advice, a treatment recommendation, or an endorsement of any specific research protocol. Always work under the supervision of a licensed professional and comply with all applicable local laws and institutional regulations when handling research peptides. The author and publisher accept no liability for any actions taken based on the information in this article.
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