Can you take a ibuprofen every 4 hours?

Yes you can take 800mg safely - as long as you aren't taking any other pain medications. And I believe it should be every 6-8hr for that amount of ibuprofin.

You cannot MIX ibuprofin & Tylenol. This will damage your kidney's. Consult your doctor, and confirm this. It's ok to take 800mg of ibuprofin. But at that level of pain medicine, Tylenol would be unnecessary anyway. If you need such medications, then over-the-counter isn't even going to work for you- go to a doctor and get proper medications. Don't be foolish, A kidney failure is far worse than ANY sinus infection. Take care fo yourself, and get well.

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Drug companies establish dosing ranges to ensure patient safety. It is possible to overdose on over the counter (OTC) pain medications without having any extra pain relief. This means that extra pain medication can harm your kidneys and/or your liver, without any extra pain relief.

400mg of ibuprofen (2 normal tabs, or 1 extra strength tab) every 4-6 hours, and up to 1000 mg of acetaminophen (2 extra strength tabs) are the upper recommended dose for both drugs. They can be taken together for maximum pain control since they are excreted through different organs, or taken intermittenly for continual pain relief (e.g. spacing your doses so that you are taking something every 2 hours, alternating whether it is advil or Tylenol).