An antacid is any substance that counteracts stomach acidity. It is taken by mouth to relieve heartburn, sour stomach, or acid indigestion. Most antacids buffer gastric acid, raising the pH to reduce acid damage. If antacids are ineffective, medication (H2-receptor antagonist]]s or proton pump inhibitors) may relieve the symptoms. Poor response to medication may be a reason to suspect an underlying medical condition.

Antacids 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®)