Some drugs suppress appetite. Pain medications, such as tylox, can cause constipation. Antibiotics can produce diarrhea. Nausea, vomiting or dry mouth are side effects of some drugs. Aspirin and motrin can irritate the stomach lining and cause discomfort.
Chemotherapy can alter taste sensation so that food seems bitter or totally bland.
Headaches, nausea, diarrhea, and eventually liver and bone damage can be caused by ingesting too much vitamin A. High doses of vitamin D can cause kidney damage and even death. Excessive amounts of supplemental iron can build up to harmful levels in the liver and other body organs. Some supplements have no nutritional value whatsover. Food can enhance or impair the absorption of a drug and alter the way it is metabolized in the body. All medications should be taken with a full glass of water or other allowed liquid.