You have to get him to stop snorting medications immediately! Snorting powdered medications is the most dangerous and life-threatening of all addictions. The problem is the inert filler, which becomes deposited in the alveoli. Years or a decade later the symptoms appear, which are non-reversible. The outcome is no different than someone exposed to asbestos. Air hunger, life on an oxygen tank, prednisone every day, and eventually being bedridden unable to walk.
Again it is "prescription" medicine. Are you saying that some doctor is fueling his addiction? If so, I would report him. Cutting off your husband's supply might force him into rehab, and hopefully put a damper on one doctor's unethical practices. There might be resulting domestic rows, but that might not be such a bad thing. The problem would be out in the open.
Does he see the problem? If not, it'll be hard to help, because he's the one who has to change. Breaking addictions isn't something lacking in the literature out there, so invest in some books or go talk to a psychologist about how to handle this. And be careful -- stopping pharmaceuticals is very difficult and if not done slowly and carefully can lead to complications. Those drugs are dangerous. Good luck.