Which term describes the time until a drug begins to work?

• A. Duration is how long the effect lasts.
• B. Onset is the time until the drug begins to work.
• C. Bioavailability.
• D. Peak effect is the time of maximum effect.

Answer: (B)

The key idea is how quickly a drug starts producing an effect after it is given. This is called the onset—the time from administration to the first noticeable effect, which depends on how fast the drug is absorbed and reaches its site of action. Routes and formulations matter: intravenous administration often yields an immediate onset, while oral tablets can take longer as they must be dissolved and absorbed. Onset is different from how long the effect lasts (duration), how much of the drug actually enters circulation (bioavailability), or the time at which the effect is strongest (peak effect).