What is the difference between tagamet (cimetidine) and pepcid (famotidine)?

Very little: Tagamet (cimetidine), Zantac (ranitidine), Pepcid (famotidine) are h2-receptor blockers, introduced by prescription in late 70's/early 80's. All reduce acid production dose-dependently, & promote drug tolerance (requiring increasing doses of drug to block increasing # of receptors with chronic use). Otc dosing is a fraction of original prescription doses. Similar side effects, efficacy, duration.

Same class: Same class of medication so very similar.