Cimetidine (Tagamet ®) is a medicine that is available as prescription medication and as an over-the-counter drug. It is used to treat several conditions related to the esophagus, stomach, and intestines. It is part of a class of drugs known as H2 blockers.imetidine (Tagamet ®) is a medicine that is available as prescription medication and as an over-the-counter drug. It is used to treat several conditions related to the esophagus, stomach, and intestines. It is part of a class of drugs known as H2 blockers.