Sodium bicarbonate reduces stomach acid. It is used as an antacid to treat heartburn, indigestion, and upset stomach. Sodium bicarbonate is a very quick-acting antacid. It should be used only for temporary relief. If you need to treat long-term stomach acid problems (such as peptic ulcer disease, GERD), talk with your doctor about other medications. Sodium bicarbonate is the active ingredient in baking soda.