As to your question, most pain medications are very constipating and it is usually necessary for patients to take stool softeners or even laxatives during treatment to stay regular. If he is nauseous on the feeding tube, try gravity feeding very slowly instead of the pump, and ensure that the formula you are using is room temperature, and that he is sitting upright while feeding and for at least an hour afterwards. I used to feed in a lounge chair in front of the TV for a couple of hours (then fall asleep for a couple more upright) routinely. Your doctors should be able to rotate him onto other anti nausea drugs, but this may have less to do with their effectiveness, and more with how he is being fed. Gravity feeding is less shocking to his stomach and generates nausea less.