What is the onset of a drug?

• A. The duration of a drug's effects
• B. The time to reach peak concentration
• C. The amount of time it takes a drug to begin working
• D. The time until the drug is eliminated

Answer: (C)

The onset is the amount of time it takes for a drug to begin working after administration. It describes when you first start to feel or observe the drug’s effect, not how long the effect lasts or how high the blood concentration becomes. This is why the option that defines onset as the time to begin producing an effect is the best fit. By contrast, the duration refers to how long the effect persists; the time to reach peak concentration is about how long until the drug’s plasma level is highest (which may not align with when the effect starts); and the time until the drug is eliminated concerns clearance from the body. Onset depends on factors like route of administration and absorption, but conceptually it marks the beginning of the drug’s action.