Drug test is performed to identify if you are reacting to a drug. Most of the drug can not be tested and the only way to find the drug allergy is to expose the patient to the drug again. Some drugs like Penicillin and local anesthesia can be tested for allergy. Since alternative medicines are available usually drug challenge is not performed.
If drug allergy testing is requested then initially, a skin prick test is performed, in which a tiny amount of anesthesia is lightly pricked into the skin with a plastic applicator.
This test is performed on the arm. If you have sensitivity, a red raised itchy hive will appear on your skin within 15-20 minutes. If no reaction to prick test, you will be retested by intradermal method (ID) with incremental dose till you show positive reaction to drug or highest recommended concentration of the drug is given intramuscularly.
Intradermal test involves injecting a very small amount of the allergen under the skin on the upper arm like TB test. (Pictures in Allergy & Food Testing section)