Is it still good?
Left a pen or a mixed vial out of the fridge, or not sure how long you’ve got? Say what you have and what happened, and get a straight answer: keep it or bin it.
Updated 30 October 2026
Almost certainly fine
A short spell out, a few hours or even overnight at room temperature, is generally fine for a reconstituted peptide. It’s prolonged warmth, not a brief spell, that’s the problem. Pop it back in the fridge.
- Unopened:A sealed lyophilised (powder) vial is stable at room temperature; keep it cool, dry and out of the light. Once you mix it, it goes in the fridge.
- Bacteriostatic water:sterile for about 28 days after first use.
A guide, not a guarantee. If the liquid looks cloudy, coloured or has bits in it, don’t use it.
How the limits work
Licensed GLP-1 pens have an exact “in-use” window set by the manufacturer: the number of days the pen can be kept out of the fridge (below 30 °C) once you’ve started it. Reconstituted peptides sold for research have no official shelf life, so the honest guide is: keep them cold, and remember the bacteriostatic water is only guaranteed sterile for about 28 days after first use.
| Product | Unopened | In use |
|---|---|---|
| Mounjaro (KwikPen) | Fridge until expiry | 30 days (fridge or below 30 °C) |
| Wegovy (FlexTouch) | Fridge until expiry | 42 days (fridge or below 30 °C) |
| Ozempic | Fridge until expiry | 42 days (fridge or below 30 °C) |
| Saxenda | Fridge until expiry | 30 days (fridge or below 30 °C) |
| A reconstituted peptide vial | Fridge until expiry | Keep cold; ~28-day BAC water window |
Common questions
- How long does Mounjaro last in the fridge?
- Unopened, it keeps in the fridge (2 to 8 °C) until the expiry date printed on it; don’t freeze it. Once you’ve started a pen, it can be kept in the fridge or below 30 °C for up to 30 days, then it should be discarded.
- How long does Wegovy last once opened?
- A Wegovy FlexTouch pen in use can be kept in the fridge or below 30 °C for up to 6 weeks, then discarded. Always check the leaflet that came with your pen.
- I left my pen out overnight. Is it still OK?
- If it stayed below 30 °C, an overnight spell is well inside the in-use window for all the GLP-1 pens, so put it back in the fridge and carry on. If it got hot (a car, direct sun), replace it to be safe.
- How long does a reconstituted peptide last in the fridge?
- There’s no official shelf life for peptides sold for research, but kept cold they’re generally considered good for a few weeks. The bacteriostatic water you mixed with is only guaranteed sterile for about 28 days after you first pierce it, which is usually what runs out first.
- I left a reconstituted vial out of the fridge. Can I still use it?
- A short spell, a few hours, even overnight at room temperature, is generally fine; it’s prolonged warmth that degrades peptides. If it sat somewhere hot, or for days, a fresh vial is the safer bet.
- Can I freeze it?
- Unopened GLP-1 pens must not be frozen; freezing damages them, and a pen that’s been frozen should not be used. Reconstituted peptides are usually kept refrigerated rather than frozen; repeated freezing and thawing is best avoided.