An antacid is a substance that is swallowed in order to buffer gastric acid, raising the pH to reduce acid damage and relieve heartburn. Some also adsorb bile salts. Common types are:

• Aluminium hydroxide (Amphojel^®, AlternaGEL^®)
• Magnesium hydroxide (Phillips’^® Milk of Magnesia)
• Aluminium hydroxide and magnesium hydroxide (Maalox^®, Mylanta^®)
• Aluminium carbonate gel (Basajel^®)
• Calcium carbonate (Tums^®, Titralac^®, Calcium Rich Rolaids^®)
• Sodium bicarbonate (Bicarbonate of soda)
• Hydrotalcite (Mg₆Al₂(CO₃)(OH)₁₆ · 4(H₂O); Talcid®)