You discharged him for asking for more pain medication? That doesn't make sense.
Also, I think the whole conversation is messed up. If you gave the maximum allowed by law and want to give more, blame the government who made the law. Tell him to write his congressman. If he is taking more opiates than prescribed, then it's his fault, not other "addicts", not the government, and certainly not yours. Do you really think that he "needs" opiates in a "decent supply" to "hold him over"? What is this? 2005?
Regarding the nurse, thank her for her opinion and move on.