Zantac 75 12 tablets are used to treat and prevent indigestion and heartburn lasting for up to 12 hours your stomach produces acid which in turn helps to digest food and on some occasions your stomach produces too much acid causing indigestion heartburn and the discomfort associated with these the active ingredient in zantac is ranitidine which is a medicine called an h2 blocker this works by preventing your stomach producing too much acid bulk pack available save up to 13 off rrp f