Which term means the opposite of the expected effect?

• A. Idiosyncrasy
• B. Tolerance
• C. Cumulation
• D. Potentiation

Answer: (A)

Unpredictable, unusual drug reactions that don’t align with the expected dose-response fall under idiosyncrasy. This means a person experiences a response that is not only different from the usual effect but can even be opposite to what the drug is intended to do. These reactions are not about how much drug is given; they come from individual differences in genetics or metabolism that make the body's response atypical. That’s why idiosyncrasy is the best match for the idea of an opposite or unexpected effect.

Tolerance refers to a diminished response after repeated doses, cumulation to the buildup of drug in the body from dosing before clearance, and potentiation to one drug increasing the effect of another.