The math for this vial
- Concentration: 5 mg ÷ 2 mL = 2.5 mg/mL (2,500 mcg/mL).
- Volume of one U-100 unit: 1 ÷ 100 = 0.01 mL.
- Mass in one unit: 2,500 mcg/mL × 0.01 mL = 25 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: 62.5 mcg at 2 mL. See U-100 vs U-40 units.
Unit chart
What common U-100 readings hold from a 5 mg vial, by water volume.
| Units | mL | 1 mL water | 2 mL water |
|---|---|---|---|
| 1 | 0.01 | 50 mcg | 25 mcg |
| 5 | 0.05 | 250 mcg | 125 mcg |
| 10 | 0.1 | 500 mcg | 250 mcg |
| 20 | 0.2 | 1 mg | 500 mcg |
| 25 | 0.25 | 1.25 mg | 625 mcg |
| 50 | 0.5 | 2.5 mg | 1.25 mg |
| 100 | 1 | 5 mg | 2.5 mg |
About this vial size
5 mg is a mid-size TB-500 vial. Across the water volumes above, one U-100 unit holds between 25 mcg (at 2 mL) and 50 mcg (at 1 mL). Compared with a 2 mg vial at the same water volume, it is 2.5 times as concentrated, so the same mass takes 0.4 times the units. A 10 mg vial at the same water volume is 2 times as concentrated as this one.
"TB-500" is used for two different molecules. Originally it named a short synthetic fragment of thymosin beta-4 (Ac-LKKTETQ, about 889 g/mol). Many products sold today are labeled TB-500 but contain full-length thymosin beta-4 (43 amino acids, about 4,963 g/mol). The vial math is identical by mass, but 5 mg of the fragment is about 5.6 times as many molecules as 5 mg of the full protein.
Storage and handling
- No approved label and no validated stability data exist for reconstituted TB-500 or research thymosin beta-4.
- General peptide practice: sealed vials cold and dark; once reconstituted, refrigerate (2-8 °C), avoid freezing, label with date and concentration.
TB-500 is not an approved drug. A 2026 advisory vote recommended it for the pharmacy compounding list, but that requires rulemaking. WADA bans it at all times.