A thread at TrailForums chats up the pluses/minuses of Vitamin I and other over-the-counter pain relievers. Something I had never heard before:

As for Tylenol, please keep in mind that the margin of safety with this drug is quite narrow, so you should be very careful with it, too. If you take Tylenol, be very careful that there is no additional acetominophen in any other meds you are taking (cold meds, Rx pain meds, etc.). Acetominophen will destroy your liver PDQ if you go over the rec. dosage, and is a common cause of acute liver failure.

Bottom line on all these things: avoid combining, don’t over-use, and check with medical authority (rather than, say, the author of a hiking blog) before packing your stuff for a long trip.

I never use pain relievers because suffering always gives me something to write about on my weekly hike write-ups.