Tramadol
"CAUTION!  Used tramadol 50 mg for back pain. Started with 1 tab couple of days/wk, eventually up to a tab/day, finally tab/day and 2 tabs/day a couple days/week. Withdrawal would kick in about 18-24 hrs after last dose. Lethargy, tired, felt like the flu. Took tab, w/in an hour felt great. Read about this as potential problem, began to wean myself off. Took several months. Every step down resulted in above withdrawal symptoms (but worse), and the most horrible part was the restless body (RLS, but all over) at night when trying to sleep. Felt ready to explode. After taking 1/4 tab/day for weeks, used some leftover partial valium tabs to finally break free from tramadol.  Avoid tramadol if at all possible - withdrawal is absolutely horrible."