- Patient has had continual pain for at least 6 months prior to inclusion in the study. This includes pain that has persisted despite conventional treatment, defined as any one of the following medications taken daily during the preceding month:acetaminophen (2- 4 grams per day)maximum tolerated and recommended doses of an NSAID, acetaminophen/codeine combination (i.e. Tylenol No 2, 3, 4) taken at least 3 times daily