Antacids are medications that neutralize excessive stomach acid and help relieve symptoms related to heartburn (burning sensation caused by acid reflux into the lower end of the esophagus), sour stomach and acid indigestion (generalized abdominal discomfort). Some antacids also relieve symptoms related to stomach ulcers or duodenal ulcers.

The body needs to maintain a proper balance between its interior acidity and alkalinity. This is known as the body’s acid-base balance. The pH scale offers a measure of the acidity or alkalinity of the body’s blood – pH stands for potential of hydrogen. The scale ranges from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. The body properly functions at a pH of about 7.4. However, the stomach is much more acidic than the rest of the body with a normal pH of less than 4. Failure to maintain a proper acid-base balance can result in various symptoms.

Antacids are intended to treat digestive upset by raising the pH level of the stomach from a highly acidic 2 to between 3 and 4. This can neutralize up to 99 percent of the acid in the stomach, leading to substantial relief from symptoms for most people. Antacids begin to work within a minute, and can provide relief that ranges from 10 minutes to more than 90 minutes.

Antacids are one of two major methods of treating digestive upset. The other involves histamine-2 (H2) blockers or proton-pump inhibitors (PPIs), which reduce the amount of acid produced in the stomach. Antacids tend to work more quickly than H2 blockers and PPIs, but the H2 blockers and PPIs provide longer-lasting relief.

Antacids are often used to treat mild to moderate forms of indigestion and heartburn, although they are less effective in treating frequent or severe forms of these symptoms. Antacids may also be used to treat conditions such as gastroesophageal reflux disease (GERD), peptic ulcers, gastritis and excess stomach gas (see Conditions treated).

Although antacids can often relieve symptoms of digestive upset, it is important to note that these symptoms may mask more serious conditions. For example, heart disease can sometimes cause symptoms of acute indigestion. Therefore, patients who experience symptoms of digestive upset for more than two weeks should consult a physician.