Lyophilized peptide is shelf-stable for years. Once you add water, the clock starts. The good news: most peptides are tougher than the internet says. The better news: a couple of simple rules cover almost every case.
Before reconstitution
Peptide powder, sealed in its original vial, stored in a cool dark place: stable for a long time. The freezer is overkill for most people. A drawer is fine. Direct sunlight and heat are the enemies — keep it out of a hot car, off a sunny shelf, away from the stove.
Why bacteriostatic water
BAC water is sterile water that contains 0.9% benzyl alcohol. The benzyl alcohol suppresses microbial growth in the reconstituted vial, which is the whole point — sterile water from an ampule has no preservative and would be safe for one draw, then start incubating bacteria. BAC water buys you a meaningful working window under refrigeration, typically 1–2 weeks in practice, with 28 days as the outer ceiling.
The 28-day rule
After reconstitution, store the vial in the fridge and use it within 28 days. That’s the outer ceiling — the absolute maximum for any multi-dose vial preserved with benzyl alcohol. In practice, the comfortable window is shorter: one week is conservative, two weeks is where most protocols land. After that, microbial contamination risk climbs and some peptides — particularly fragile ones like GH fragment — can also degrade chemically, turning the solution thick or cloudy. Both peptide potency and sterility are on the clock.
If you have a 10 mg vial and you’re drawing 250 mcg/day, you’ll finish it in 40 days — well over the line. Size your reconstitution to match your use rate: reconstitute smaller volumes (2–3 mL instead of 5 mL) so you burn through a vial in 1–2 weeks and never have to wonder.
Signs the vial is bad
- Cloudiness after the initial swirl. Most reconstituted peptides are clear. Cloudy means precipitate or contamination.
- Color change. Most peptides are colorless. GHK-Cu is the famous exception — it’s blue, because of the copper. If a clear peptide turns yellow or brown, throw it out.
- Visible particles floating in the solution.
- Off smell if the seal has been compromised.
When in doubt, throw it out. Peptides are not so expensive that you should risk an injection-site infection to save $40.
Sanitization, briefly
Always swab the rubber stopper with a 70% isopropyl alcohol pad before puncturing it — both when reconstituting and when drawing each dose. Wait a few seconds for the alcohol to dry. Don’t swab the needle itself.
Travel
Domestic flights in the US: peptides go in checked bags or carry-on without issue. TSA does not care. International travel: research the destination’s laws — most countries are fine with personal-use quantities in checked luggage, but a few are not. A doctor’s note never hurts.
One more rule
Don’t shake reconstituted vials. Swirl gently between your palms. Vigorous shaking can denature peptides and create foam that’s annoying to draw. The dissolution is mostly diffusion-driven and takes a few minutes.
For the math behind your draw, use the reconstitution calculator. For full protocols on every peptide, get the free Peptide Guide.