When reconstituting peptides, one of the most critical decisions you’ll make is choosing between bacteriostatic water (BAC) and normal saline (0.9% NaCl). Our decay calculator applies a 1.5x multiplier to saline-based reconstitutions—but why?

The Science Behind the 1.5x Rule

Bacterial Growth Factor

Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth. This preservative effect extends beyond just preventing contamination—it also slows down peptide degradation by:

Reducing oxidative stress from bacterial metabolites
Stabilizing pH over longer storage periods
Minimizing enzymatic breakdown from trace contaminants

Normal saline lacks this protective agent, making peptides more vulnerable to degradation from:

Bacterial contamination (even in sterile conditions, microbes can enter during dosing)
pH shifts due to CO2 absorption
Oxidation from trace metal ions in the saline solution

Clinical Data Supporting the 1.5x Rule

While limited head-to-head studies exist for all peptides, research on insulin stability (structurally similar to many research peptides) shows:

BAC-reconstituted insulin: Stable for 28 days at 2-8°C
Saline-reconstituted insulin: Stable for 14-21 days at 2-8°C

This translates to approximately 1.3-2x faster degradation with saline, aligning with our conservative 1.5x multiplier.

Real-World Observations

Community data from peptide researchers consistently shows:

BPC-157 Example

BAC Water (Fridge): Maintains >80% potency for 30+ days
Saline (Fridge): Noticeable potency loss after 20 days

Semaglutide (GLP-1)

BAC Water (Fridge): 4-week stability (per manufacturer guidelines)
Saline (Fridge): Often shows clouding/precipitation by day 21

When to Use Each Solvent

Use Bacteriostatic Water When:

✅ Long-term storage needed (>2 weeks)
✅ Multiple-dose vials (repeated needle punctures)
✅ Fragile peptides (GLP-1s, growth hormone analogs)
✅ Maximum potency preservation is priority

Use Saline When:

⚠️ Benzyl alcohol allergy present
⚠️ Single-dose administration planned
⚠️ BAC water unavailable (emergency only)

Practical Recommendations

Default to BAC Water: Unless contraindicated, bacteriostatic water is the gold standard for peptide reconstitution.
Adjust Your Expectations: If using saline, plan to use the peptide 33% faster or accept reduced potency.
Monitor Visual Changes: Saline-reconstituted peptides may show clouding, precipitation, or discoloration sooner—these are signs of degradation.
Consider Smaller Vials: If BAC water isn’t an option, reconstitute in smaller volumes to ensure faster use.

Calculator Implementation

Our Potency Decay Calculator automatically accounts for solvent choice:

Saline Decay Rate = BAC Decay Rate × 1.5

For example:

BPC-157 in BAC (Fridge): 2% daily decay
BPC-157 in Saline (Fridge): 3% daily decay

This conservative approach ensures you’re never overestimating remaining potency.

Conclusion

The 1.5x decay multiplier for saline isn’t arbitrary—it’s based on a combination of:

Clinical insulin stability data
Community observations across multiple peptides
Conservative safety margins

While bacteriostatic water is strongly preferred, understanding the trade-offs allows for informed decision-making when alternatives are necessary.

Related Tools:

References:

Insulin Stability Studies - American Diabetes Association
Bacteriostatic Agents in Injectable Solutions - FDA Guidelines
Community Stability Reports - Peptide Sciences Database

Bacteriostatic Water vs Saline: The 1.5x Decay Rule Explained