In rare cases, people who have taken antacids that include calcium carbonate have developed hypercalcemia, or excess calcium in the bloodstream. Tums, Alka-2 and Titralac are three brands that use calcium carbonate as their active ingredient, as stated by The New York Times.
Antacids containing calcium carbonate only cause hypercalcemia after prolonged periods of use. This condition can cause kidney failure, which can be life-threatening. Antacids that use other active ingredients do not pose the same threat. For example, antacids with aluminum salts as their active ingredient, such as Alternagel or Amphogel, have the potential side effect of calcium loss, which can cause osteoporosis over time, notes The New York Times.
Magnesium salts are another common active ingredient in antacids. Milk of Magnesia uses magnesium hydroxide, while Maalox and Mylanta use a combination of aluminum and magnesium salts. With magnesium salts, the primary side effect is diarrhea, which is why some antacids combine it with aluminum, which tends to cause constipation, according to The New York Times.
In general, antacids neutralize acidity in the digestive system and relieve occasional outbreaks of heartburn. Relying on these medications for long periods of time can lead to kidney disease or osteoporosis, depending on the active ingredient, as stated by The New York Times.