That's how most of the '-contin' formulations work (eg oxycontin). You make tiny pellets of the analgesic, add a thin layer of wax to some, a thicker layer to some, a thicker yet layer to some, then make up a pill containing some pellets with no coating, and some with each of the increasingly thicker layers of wax. When you swallow the pill, the stuff with no layer goes into immediate effect (so you get fast acting relief). The acid in your stomach starts dissolving the wax around the rest, with the different thicknesses of wax acting to give a continuous release of the remaining analgesic. Different formulations have differing amounts of the initial uncoated analgesic.