After you take an aspirin, for how long does it thin your blood?

Platelets. Aspirin irreversibly inhibits platelets, the life of a platelet is up to 10 days, so you can see effects of asa for up to 10 days from the time it was stopped.
7 to 10 days. Aspirin affects your platelet function. Platelets are the first cells to stop bleeding. They form a plug to stop further bleeding. Once you take Aspirin takes on average about 7 days to 14 days to have platelets resume their normal function providing one is also not taking advil, motrin, ibuprofen, Naproxen as well.