Paradoxical reaction to a drug could be defined as:

A paradoxical reaction to a drug is the opposite of what one would expect, such as becoming agitated by a sedative or sedated by a stimulant. Some are common and are used regularly in medicine, such as the use of stimulants such as Adderall and Ritalin in the treatment of attention deficit hyperactivity disorder (also known as ADHD or ADD), while others are rare and can be dangerous, as they are not expected, such as severe agitation from a benzodiazepine.