<qa>  What is the duration of pain?OUTLINE: This is a randomized, double-blind, placebo-controlled study. Patients are stratified according to etiology of pain breast surgery vs lung surgery vs amputation vs other, duration of pain 1-3 months vs 4-6 months vs more than 6 months, and current analgesic regimen opioids including tramadol vs antidepressants vs anticonvulsants vs combination vs other vs none. Patients are randomized to 1 of 2 treatment arms. 