Patients with low back pain who are sub-optimally responsive to their current analgesic treatment begin open-label treatment with oxymorphone extended release (ER). During the Open-Label Titration Period, patients will receive daily oxymorphone ER by mouth (PO) q12h. The investigator will initiate the Open-Label Titration Period using study drug at a dose of 5 mg PO q12h for 2 days; thereafter, patients will continue receiving 5 mg q12h or be titrated at increments of 5-10 mg q12h every 3-7 days until stabilization is achieved. The goal of the Open-Label Titration Period is to determine for each patient a fixed dose of study medication that is tolerated and achieves adequate analgesia. Stabilized patients will be randomiozed to either continue with current dose of oxymorphone ER or receive placebo for a total duration of 12 weeks.