Definition: Freeze-thaw is a cycle of a liquid drug freezing and then warming back into a liquid. For peptide and protein drugs in solution, freezing can damage part of the drug, mainly by unfolding and clumping at the surface of ice crystals. Labels for liquid products such as Wegovy, Forteo and Humulin R say do not freeze.
| Product | What the label says |
|---|---|
| Wegovy (semaglutide) | Do not freeze and do not use if frozen. Do not store in the freezer or directly next to the refrigerator cooling element. |
| Forteo (teriparatide) | Do not freeze. Do not use if it has been frozen. |
| Humulin R (insulin) | Do not freeze. Do not use if it has been frozen. |
| Omnitrope (somatropin) | Store vials and cartridges in the refrigerator. Do not freeze. |
None of these labels describes a way to use a product after it has frozen. The Forteo instructions say to throw a frozen pen away and use a new one.
A 2025 review explains the stresses (Li 2025). As water turns to ice, the drug and the other ingredients are pushed out of the ice into a smaller, more concentrated pocket of liquid. Temperature, pH and salt levels in that pocket shift. Protein molecules can stick to the ice surface, unfold and then clump. Very cold temperatures can also unfold some proteins directly.
Drug makers do freeze some protein solutions on purpose, for example as the first step of freeze-drying. They control the freezing and thawing rates and add stabilizers such as sugars, surfactants and amino acids. A home freezer offers none of that control.
A thawed vial or pen can look exactly as it did before. Damage from clumping can be too small to see (see aggregation), which is why labels say not to use a product that has been frozen rather than telling you to check it. Freeze-dried powder is a different case; see lyophilized.
Read more on Dose Track: Can you freeze peptides? · Peptide left out of the fridge · Traveling with injectables