Peptides are sensitive to heat, light, and time. How you store them before and after mixing is the main thing that determines how long they stay usable, and the window differs from compound to compound.
Reviewed for accuracy · Last reviewed July 7, 2026Freeze-dried (lyophilized) peptide powder is the most stable form. It is usually kept refrigerated and away from light, and some products tolerate short periods at room temperature during shipping. Long-term, cold and dark is the safe default.
Once mixed, a peptide is far less stable and belongs in the refrigerator, not the freezer, since freezing and thawing can damage some peptides. Many reconstituted peptides are kept for roughly 2 to 4 weeks, but the exact window is compound-specific. Tesamorelin, for example, is often cited as less stable once mixed than the GLP-1 peptides.
Keep the vial out of direct light, label it with the date you mixed it, and discard it if the solution becomes cloudy or shows particles (color alone is not always a problem: reconstituted GHK-Cu is normally deep blue from its copper).
Branded and compounded GLP-1 products are generally refrigerated, though many labels allow a limited number of days at room temperature. People often ask how long tirzepatide or semaglutide can sit out of the fridge; the honest answer is that it depends on the specific product, and the product's own instructions are the authority. When in doubt, keep it cold.