XR - Extended Release They are coated in layers so that each layer carries with it an inherent absorption time thus cutting back on the number of times one needs to dose themselves within a day and increasing patient compliance. If you crush the pill up, those layers are broken up and the whole pill is absorbed at once, giving you more medicine than was intended. An example would be Oxycontin which is like an Oxycodone XR of sorts. Hope that helps.