Some really strong pain killers can have a negative effect. I know someone who actually get stomach ulcers from them because of how bad her pain is. She still takes them, but she just have to moderate what she eats and how often she takes them. If your experience pain or sickness, maybe consider changing your medicine, especially if they are very strong pain killers. Often times those type of pain killers are taken with food too, so it reduces damage on your intestines, so maybe just check if you should have food first.