Gaviscon Extra Chewable Tablets (48). Gaviscon Extra Chewable Tablets are a combination of two antacids (calcium carbonate and sodium bicarbonate) and an alginate.. This medicine works in two ways:. Neutralising excess stomach acid to relieve the pain and discomfort.. Forming a protective barrier of the stomach contents to soothe the burning pain in your chest which may last for up to 4 hours.. This medicine is used for the treatment of acid related symptoms of gastro-oesophageal reflux such as acid regurgitation, heartburn and indigestion which may occur, for example, following meals or during pregnancy.