Rennie Spearmint tablets contain two antacids called calcium carbonate and magnesium carbonate which neutralise stomach acid by turning it into water. They act directly in the oesophagus as well as in the stomach and are then eliminated by your body. The usual dosage is 1 to 2 tablets initially, up to 3-4 times per day. In case of more frequent or severe pain, the dose may be increased for a short period, up to 12 tablets per day. This medicine is suitable for adults and children over 12 years. The duration of treatment is limited to 14 days.