Try never to mix any over the counter pain relievers in the same day. If you take aspirin, then continue with aspirin in that twenty-four-hour period. If you prefer ibuprofen, then stay with that particular pain reliever. The same advice goes for acetaminophen. Switching between aspirin to ibuprofen or say ibuprofen to acetaminophen can potentially harm your liver. The safest advice is to stick to one choice and take the recommended amount.