The trial includes a 2 week titration phase starting with either 45 mg Morphine Sulfate Controlled Release (CR) twice daily or 100 mg tapentadol ER taken twice daily (bid). Based on effectiveness and side effects participants can up-titrate in steps of 50 mg Tapentadol ER or 15 mg Morphine Sulfate CR to a maximal dose of 250 mg Tapentadol ER bid or 90 mg Morphine Sulfate CR twice daily respectively. If subjects meet the stabilization criteria at the end of the titration phase they will be re-randomized to either placebo or active treatment and will continue 4 weeks at the last dose level in the maintenance phase.