verb: (medicine, pharmacology) To try a therapeutic pharmaceutical drug, suspected allergen, or medical treatment on a patient a second or subsequent time, to see if the suspected effects of the treatment occur again. This is typically performed to confirm allergic or adverse reactions to allergens or medications, but may also be used to confirm beneficial treatments or to retry a probable beneficial treatment which did not appear to be effective previously.
noun: A challenge made in return.
noun: (medicine, pharmacology) The event of rechallenging as above.
