Worked example
Add 2 mL of water to a vial holding 10 mg of Retatrutide. The concentration is 10 ÷ 2 = 5 mg/mL, or 5,000 mcg in every millilitre. On a U-100 syringe, where 100 units make 1 mL, each unit holds 50 mcg and each 10 units hold 500 mcg.
Change the water and only the concentration changes. With 4 mL instead, each 10 units hold 250 mcg, half as much, and any given mass takes twice the units to measure. These numbers illustrate the arithmetic; they are not amounts to use.
Concentration table
Common Retatrutide vial sizes against common water volumes. The last column is what 10 units on a U-100 syringe hold.
| Vial | Water | Concentration | 10 units (U-100) hold |
|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 500 mcg |
| 5 mg | 2 mL | 2.5 mg/mL | 250 mcg |
| 5 mg | 3 mL | 1.667 mg/mL | 166.7 mcg |
| 10 mg | 1 mL | 10 mg/mL | 1 mg |
| 10 mg | 2 mL | 5 mg/mL | 500 mcg |
| 10 mg | 3 mL | 3.333 mg/mL | 333.3 mcg |
| 15 mg | 1 mL | 15 mg/mL | 1.5 mg |
| 15 mg | 2 mL | 7.5 mg/mL | 750 mcg |
| 15 mg | 3 mL | 5 mg/mL | 500 mcg |
| 20 mg | 1 mL | 20 mg/mL | 2 mg |
| 20 mg | 2 mL | 10 mg/mL | 1 mg |
| 20 mg | 3 mL | 6.667 mg/mL | 666.7 mcg |
| 30 mg | 1 mL | 30 mg/mL | 3 mg |
| 30 mg | 2 mL | 15 mg/mL | 1.5 mg |
| 30 mg | 3 mL | 10 mg/mL | 1 mg |
Notes for Retatrutide vial math
- Vial sizes for retatrutide span a wide range, so the same volume of water gives very different concentrations. 2 mL in a 5 mg vial is 2.5 mg/mL; 2 mL in a 30 mg vial is 15 mg/mL, six times stronger. Re-check the vial size every time; it is the most common input mistake.
- At high concentrations a small reading error is a large mass error. At 15 mg/mL, one unit on a U-100 syringe holds 150 mcg. Adding more diluent lowers the concentration and spreads the same mass over more graduations, which is easier to read.
- Only Eli Lilly makes retatrutide. Products sold online as "reta", "GLP-3" or similar names are not Lilly's investigational drug, and their identity and content are unverified unless independently tested.
Storage and handling
- No approved label exists for retatrutide, so there is no official storage or in-use stability data. Published stability data for reconstituted research material is also absent.
- General lab practice for lyophilized peptides: store sealed vials cold and away from light; after reconstitution keep the vial refrigerated (2-8 °C), do not freeze it, and label it with the date and concentration.