Antacids are common over-the-counter remedies that settle acids in your stomach. Many antacids contain bases, however there are some that are acid acid based, like milk of magnesia.
Antacids work by counter-acting the acids in your stomach. They do this because most of the ingredients are bases, and bases are the opposite of acids.
Many antacid users can experience headache, nausea, and constipation. These side effects are extremely uncommon and have had any in-depth study performed on them
Common antacids include, milk of magnesia, magnesium carbonate, and calcium carbonate.