An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Every base can neutlize acids. (In that sense all bases are antacids).But we cannot take all bases. Because our body can tolerate only bases in mild concentrations. And also we should ensure that the bases are not toxic and does not have any harmfull side effects. So all bases cannot be called antacids. Antacids include aluminium hydroxide, magnesium carbonate and magnesium trisilicate. These are used in mild concentrations