What is the approximate onset of action for acetaminophen after administration?

• A. Immediately
• B. 2-3 hours
• C. About 30 minutes
• D. 6-8 hours

Answer: (C)

Onset of action for acetaminophen given by mouth is about 30 minutes. After you take it, the drug has to be absorbed from the gut into the bloodstream and reach the central nervous system where it produces analgesic and antipyretic effects. This absorption-and-distribution process means you typically start to feel relief around the 30-minute mark, with peak effects usually occurring within 1–3 hours and total duration of about 4–6 hours. Immediate relief isn’t expected because there’s a necessary delay for absorption; waiting 2–3 hours is longer than the usual onset, and 6–8 hours reflects how long the drug lasts, not when it begins. Note that if acetaminophen is given intravenously, onset can be faster, but for standard oral dosing the approximate onset is around 30 minutes.