What is the duration of aspirin's effect?

• A. 2-4 hours
• B. 4-6 hours
• C. 8-12 hours
• D. 24 hours

Answer: (B)

The key idea is that “duration of effect” depends on which effect of aspirin you’re considering. For pain relief and fever reduction, aspirin’s symptomatic effect lasts about 4 to 6 hours. After that window, relief typically wanes as the drug is cleared from the bloodstream and its direct analgesic/antipyretic action diminishes.

It’s important to contrast this with its antiplatelet action: aspirin irreversibly inhibits COX-1 in platelets, and since platelets can’t synthesize new COX-1, the antiplatelet effect lasts for the life of a platelet—about 7 to 10 days. So while the analgesic effect is roughly 4–6 hours, the platelet-inhibition effect extends much longer, which is clinically important for bleeding risk and timing around procedures. In the question’s context, the duration being asked about is the analgesic/antipyretic effect, hence about 4–6 hours.