Antacids (or indigestion tablets) are used to help stop indigestion. People may get indigestion if they eat too much or if they have eaten too fast. With indigestion, the liquid in the stomach will become more acidic. Antacids will neutralise the acids. The reaction that is happening is called neutralisation. This is because the tablets are alkaline and the liquids in the stomach are acidic.
This reaction between the stomach acids and the antacid will make the acid change into harmless substances such as water or salt.
An example of an antacid is milk of magnesia.
Side effects from taking antacids are rare, but can include both constipation and diarrhea. They are also high in sodium so people with a heart condition on a low salt diet should ask their doctor before taking them.