Ball-and-stick model of cimetidine, the prototypical H 2 -receptor antagonist. The H2 receptor antagonists are a class of drugs used to block the action of histamine on parietal cells (specifically the histamine H2 receptors) in the stomach, decreasing the production of acid by these cells.he H 2 antagonists are competitive antagonists of histamine at the parietal cell H 2 receptor. They suppress the normal secretion of acid by parietal cells and the meal-stimulated secretion of acid.