Ranitidine bismuth citrate can cause the tongue to darken and stools to turn black.
H2 receptor antagonists e.g. cimetidine, famotidine, nizatidine, ranitidine.
ingredient ranitidine hydrochloride, which is a type of medicine called an H2-receptor antagonist.
Common H2 blockers are nizatidine (Axid), ranitidine (Zantac), famotidine (Pepcid), and cimetidine (Tagamet).