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According to my doctor, 4 hours. You can switch them up. Take acetaminophen, (Tylenol), then wait 4 hours and take Ibuprofen, wait another 4 hours and take acetaminophen and so on. :) 15 people found this useful.
Depending on what painkiller, and why. If it's another NSAID, you should wait around 4 to 6 hours unless the dose of ibuprofen was low e.g. 200 mg. As for ibuprofen, if the pain didn't lessen after taking a dose of ibuprofen, if no stomach ache I would prefer one taking more ibuprofen up to maximum of 800 mg in total.