The math for this vial
- Concentration: 20 mg ÷ 2 mL = 10 mg/mL (10,000 mcg/mL).
- Volume of one U-100 unit: 1 ÷ 100 = 0.01 mL.
- Mass in one unit: 10,000 mcg/mL × 0.01 mL = 100 mcg.
- The whole vial is 200 U-100 units of solution, more than one 1 mL syringe holds.
On a U-40 syringe each unit is 0.025 mL, so each unit holds 2.5 times as much: 250 mcg at 2 mL. See U-100 vs U-40 units.
Unit chart
What common U-100 readings hold from a 20 mg vial, by water volume.
| Units | mL | 1 mL water | 2 mL water | 3 mL water |
|---|---|---|---|---|
| 1 | 0.01 | 200 mcg | 100 mcg | 66.7 mcg |
| 5 | 0.05 | 1 mg | 500 mcg | 333.3 mcg |
| 10 | 0.1 | 2 mg | 1 mg | 666.7 mcg |
| 20 | 0.2 | 4 mg | 2 mg | 1.333 mg |
| 25 | 0.25 | 5 mg | 2.5 mg | 1.667 mg |
| 50 | 0.5 | 10 mg | 5 mg | 3.333 mg |
| 100 | 1 | 20 mg | 10 mg | 6.667 mg |
About this vial size
20 mg is a mid-size Retatrutide vial. Across the water volumes above, one U-100 unit holds between 66.7 mcg (at 3 mL) and 200 mcg (at 1 mL). Compared with a 15 mg vial at the same water volume, it is 1.33 times as concentrated, so the same mass takes 0.75 times the units. A 30 mg vial at the same water volume is 1.5 times as concentrated as this one.
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.
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.
Retatrutide is an investigational Eli Lilly drug in Phase 3 trials. It is not FDA-approved, cannot be legally compounded, and FDA has issued warning letters to online sellers of "research" retatrutide.