I take OxyContin MR tablets for severe back-pain. I've recently switched from MST MR tablets which used to provide relatively balanced pain-relief for the expected 12 hour period. However, I'm finding that OxyContin tablets are ceasing to be effective after only 8 hours (the manufacturer claims that they provide pain-relief for 12 hours). I'm constantly struggling to keep to the prescription schedule and my GP is convinced that I'm deliberately abusing these tablets! Has anyone had a similar experience with these tablets?