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BAC water vs sterile water for peptides.
Peptides ship as a freeze-dried powder and have to be reconstituted with something liquid before you can draw a dose. The choice between bacteriostatic water (BAC) and sterile water for injection is almost always BAC for multi-dose vials and sterile for short, single-use workflows — but the edge cases matter. This page walks through the practical rule, the data for the top 15 peptides in the library, and where defaulting to BAC is a bad idea.
Quick rules
- 1BAC waterfor any vial you'll draw from more than once. The benzyl alcohol preservative keeps the solution viable through repeated needle entries.
- 2Sterile water for single-use products, intranasal sprays, and anything where benzyl alcohol contact is contraindicated (ocular, infant dosing, documented allergy).
- 3Defer to product label or pharmacy direction when they conflict with the general rule. Some compounded formulations specify a diluent for a reason that isn't obvious from the molecule alone.
Recommended diluent by peptide.
The 15 most commonly stocked peptides in our library. The "practical window" column is the realistic fridge life once reconstituted with BAC water at typical concentrations — vendor stability data, not regulatory shelf life.
| Peptide | Category | Recommended diluent | Practical window |
|---|---|---|---|
| Trofinetide | Cognitive | BAC water (nasal: sterile) | 2 weeks refrigerated |
| L-Carnosine | Longevity | BAC water | 3–4 weeks refrigerated |
| Glutathione | Longevity | BAC water | 3–4 weeks refrigerated |
| NAD+ | Metabolic | BAC water | 2–4 weeks refrigerated |
| 5-Amino-1MQ | Metabolic | BAC water | 2–4 weeks refrigerated |
| Thymopentin (TP-5) | Immune | BAC water | 2–3 weeks refrigerated |
| Dihexa | Cognitive | BAC water (nasal: sterile) | 2 weeks refrigerated |
| Orforglipron | GLP-1 | BAC water | 4–8 weeks refrigerated |
| SS-31 (Elamipretide) | Longevity | BAC water | 3–4 weeks refrigerated |
| Cerebrolysin | Cognitive | BAC water (nasal: sterile) | 2 weeks refrigerated |
| MK-677 | GH Secretagogue | BAC water | 2–3 weeks refrigerated |
| SLU-PP-332 | Metabolic | BAC water | 2–4 weeks refrigerated |
| Thymalin | Longevity | BAC water | 3–4 weeks refrigerated |
| Tirzepatide | GLP-1 | BAC water | 4–8 weeks refrigerated |
| Retatrutide | GLP-1 | BAC water | 4–8 weeks refrigerated |
Why the rule isn't "always BAC."
BAC water is sterile water with 0.9% benzyl alcohol added as a bacteriostatic preservative. The alcohol concentration is enough to suppress bacterial growth between draws but not high enough to denature most peptides.
Two situations call for sterile water instead. First, intranasal and intra-ocular routes — benzyl alcohol is irritating to mucosa and the ocular surface, so nasal sprays should use plain sterile water and be made fresh weekly. Second, neonatal or infant dosing (irrelevant to most readers but worth flagging) — benzyl alcohol crosses the blood-brain barrier disproportionately in infants.
For adult subcutaneous and intramuscular peptide injection, BAC water is the default. The preservative is the entire reason the same 5 mg vial can be drawn from for six weeks instead of one.
Educational reference only. This page is informational and does not constitute medical advice. Peptide protocols carry real clinical risk. Consult a qualified healthcare provider before reconstituting, injecting, or stacking any compound.
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