Darvocet N-100 is acetaminophen 650 mg (the equivalent of two regular-strength Tylenol) and 100 mg of propoxyphene napsylate (the equivalent of 65 mg propoxyphene sodium, which is what's in a Darvon-65). The effect of the two is partly additive, so the pain relief is better than taking two regular-strength Tylenol alone, but probably not better than taking two extra-strength Tylenol, though the propoxyphene also often gives a mild euphoric feeling that some people find useful, and some people like too much. It's something of a silly combination, because most people need to take two to get any reasonable level of pain relief, and over any period of time, that risks an acetaminophen overdose.