H2 blockers reduce the amount of acid made by your stomach. They are used in conditions where it is helpful to reduce stomach acid. For example, for acid reflux which causes heartburn. Most people who take H2 blockers do not develop any side-effects.H2 blockers are a group of medicines that reduce the amount of acid produced by the cells in the lining of the stomach. They are also called 'histamine H2-receptor antagonists' but are commonly called H2 blockers.They include cimetidine, famotidine, nizatidine and ranitidine, and have various different brand names. Your stomach normally produces acid to help with the digestion of food and to kill germs (bacteria).or example, for acid reflux which causes heartburn. Most people who take H2 blockers do not develop any side-effects. H2 blockers are a group of medicines that reduce the amount of acid produced by the cells in the lining of the stomach.