Need doctor help! how to tell if my whole family is allergic to hydrocodone?

By taking it: There is no way to know whether someone has a reaction to hydrocodone (which isn't usually a true allergy, but rather a drug side effect) outside of taking it and having a problem. Many people get flushing, itching and even hives with hydrocodone or Codeine (or other opioids) - this is from histamine release, and is a side effect and not an allergy.