Rennie is a brand of antacid tablets commonly used to relieve heartburn, indigestion, and upset stomach. The active ingredients in Rennie typically include calcium carbonate and magnesium carbonate, which work by neutralizing stomach acid. It is available in various flavors and is often used for quick relief from discomfort after meals. Rennie is widely available over-the-counter in pharmacies and supermarkets. It is suitable for adults and children over the age of 12, but it is important to follow the recommended dosage. People with certain medical conditions or those taking specific medications should consult a healthcare professional before using Rennie.