Duration of action is best described as which?

• A. The time from administration to the beginning of the therapeutic effect
• B. The time to reach peak effect
• C. The time for drug elimination
• D. The time during which a therapeutic effect can still be observed

Answer: (D)

The duration of action is the period after a drug is given during which a therapeutic effect can be observed. It starts when the effect begins and ends when the effect wears off. This timing often tracks how long the drug’s concentration stays above the level needed to produce the effect, though persistent effects can occur even as plasma levels fall.

Onset tells you when the first effect appears, time to peak is when the effect is strongest, and elimination time covers how quickly the drug is cleared from the body. Those concepts describe different aspects than how long the effect lasts.