My doctors and I have found IV and IM injections of Dilaudid work very well for me in controlling post-surgical pain, but NOTHING I take by mouth - Vicodan, Percoset, Dilaudid - give any relief at all. Someone suggested to me that it is because of a "first past" metabolic issue - that eventually the drug, whether IV, IM or oral, hits my liver, but with the IV/IM route, I have already received the pain relief before it is broken down and, at least in the case of oral meds, poorly metabolized. Does this make sense?