NSAIDS such as Ibuprofen or analgesics such as Acetaminophen work in most cases.
Medical history of the patient important.

The meds of choice are NSAID's followed by Tylenol. Narcotics are usually not necessary and prescribed in limited circumstances

Have you tried Ibuprofen? The over the counter stuff is 200 mg. It lasts for 4 hours. If you take more than 2, it will still last for only 4 hours. Time released Ibuprofen is by prescription, so you'd have to call whoever did the root canal therapy for you. Having said that, you can take 2 Ibuprofen 200 mg with 1 extra-strength Tylenol (or 500 mg acetaminophen) every 4-6 hours, as needed for pain. A word of caution. You cannot take more than A TOTAL OF 3000-4000 mg of acetaminophen or more than A TOTAL OF 3200 mg of Ibuprofen in a 24 hour time period - from all sources, with caveats. All sources include anything that has these ingredients in them, such as cold remedies, headache remedies, etc.

Start off with something over the counter like Ibuprofen or Tylenol, and if that doesn't work, contact your dentist and ask for a prescription strength pain killer.