What's the best way to know if my pain meds are causing an allergic reaction?

Challenge testing: Stopping a medication suspected of causing allergic symptoms and waiting until a reaction has subsided is the first step. If no serious allergic symptoms are experienced (dizziness, shortness of breath, throat fullnes or body tissue swelling), re-starting the medication may be the only way to determine if you are allergic. Speak to the prescribing physician before performing challenge testing.