Which statement defines tolerance?

• A. Needing higher doses over time for the same effect
• B. Anesthesia requirement
• C. Irreversible addiction
• D. A temporary side effect

Answer: (A)

Tolerance is a phenomenon where repeated exposure to a drug produces a diminished effect, so progressively larger doses are needed to achieve the same level of analgesia or psychoactive effect. This happens through adaptive changes such as receptor desensitization or downregulation and increased drug metabolism, which make the body less responsive to the same amount of drug. Therefore, needing higher doses over time for the same effect is the defining feature. Tolerance is reversible and distinct from dependence (withdrawal) and addiction (compulsive use). The other statements describe scenarios that are not how tolerance is defined: requiring more anesthesia can occur in specific contexts but isn’t the general definition; irreversible addiction implies a lasting behavioral change rather than a diminished drug response; and a temporary side effect is not about needing more drug to achieve the same effect.