Prelief is calcium glycerophosphate. Prelief contains calcium and phosphorus in the same ratio to one another as in milk. The U.S. Food and Drug Administration regards calcium glycerophosphate as "GRAS", which means Generally Recognized As Safe. What about side effects? There are none, unless you are restricted in your intake of calcium or phosphorus. Otherwise, Prelief is absolutely safe It simply changes the acid levels of food by mopping the acid up and removing it.