Which term describes the time when drug effects begin after administration?

• A. Onset of action
• B. Peak effect
• C. Duration of action
• D. Half-life

Answer: (A)

Onset of action is the interval between when a drug is given and when its first noticeable effect occurs. This is the best description because it specifically marks when the drug starts working, not how strong it becomes or how long it lasts. Peak effect refers to when the drug’s effect is strongest; duration of action is how long the effect lasts after it begins; half-life is the time it takes for the drug’s concentration in the body to fall by half, influencing how often you must dose. Onset depends on the route and rate of absorption (IV is typically rapid, oral is slower due to digestion and first-pass metabolism), and understanding it helps anticipate when a patient will begin to feel relief after a medication.