My father has severe nerve pain from diabetes damage but he won't take his pain pills. How can I convince him?

He has neuropathy because he didn't control his diabetes. He didn't take his diabetes medication. So now his legs are in severe pain. The doctor said it is siatic (sp.?) nerve pain. So what he does is he limps around the house in slow motion all day long and he is crabbier than hell because he says he is in pain. Then I ask him, "Well, are you taking your oxycodone that the doctor prescribed to you?" He says, "No. I don't want to take it. I don't like medications. I don't trust them." So what the hell can I do if a grown man won't listen to his doctor? I wouldn't normally care if he is crabby but I have to live with him. In a sense, it is kind of his own fault he is in so much pain and he shouldn't go around snapping at everyone.