If I'm allergic to codeine will I be allergic to percocet as well?

Codeine. Codeine and Percocet can both trigger itching and hives as they release histamine from the mast cells in the skin in a non-specific manner.
? tolerance issue ? In true Codeine allergy, risk of cross-reactivity w/ another opioid can be reduced if analgesic of a different class is used. There are 3 chemical classes of opioid analgesics: phenanthrenes, phenylpiperidine, & phenylheptanones (diphenylheptanes). Codeine & oxy are phenanthrenes which means risk of cross reactivity is high. However, majority do well staying in same class, unless life threatening.