Updated June 23, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

H2 blockers, also called H2-receptor antagonists, are acid-reducing medicines commonly used to treat gastroesophageal reflux disease and esophagitis, and to reduce the symptoms of peptic ulcer disease. They work by blocking an important producer of stomach acid: histamine 2.

How Do H2 Blockers Work?

A cell in the stomach, called a parietal cell, makes acid. These cells are found in the stomach lining, and are stimulated in a number of ways to produce acid.

One of these acid stimulants is methods is histamine 2. H2 Blockers reduce acid production by blocking signals that tell the stomach to make acid.

Are there Differences Among the Different H2 Blockers?

There are differences in potency. Over-the-counter formulations are the least potent doses. Among the prescription forms, Pepcid (famotidine) is the most potent H2 Blocker.

What are the different types of H2 Blockers?

Prescription forms:

• Tagamet (cimetidine)
• Pepcid (famotidine)
• Axid (nizatidine)
• Zantac (ranitidine)

Nonprescription (over the counter) forms:

• Tagamet-HB
• Pepcid-AC
• Axid AR
• Zantac 75

The non-prescription H2 blockers are formulated at lower doses than the prescription drugs.

Precautions

H2 blockers are generally very well tolerated. They occasionally produce abdominal pain, allergic reactions, palpitations or mood changes.

The biggest precaution one must take with H2 blockers is that they frequently interact with other medications. Before you use these drugs - even the OTC kind - you should check with your doctor to make sure they are safe for you.

How Are H2 Blockers Different from Proton Pump Inhibitors (PPIs)?

Both PPIs and H2 blockers suppress gastric acid secretion, but at different stages of production.. While histamine blockers block one of the first stimuli for acid production, proton pump inhibitors block the final step in the pathway of acid secretion in the stomach, resulting in greater suppression of acid.

PPIs have a delayed onset of action, while H2 Blockers begin working within an hour. PPIs work for a longer period of time; most up to 24 hours and the effects may last up to three days. H2 blockers, however, usually only work up to 12 hours.

This means that H2 blockers are most often used occasionally (when there is an acute flare-up of heartburn, for instance), while PPIs are used for longer periods of time (often, for a 2-week course of therapy) in an attempt to get a more chronic condition under control.

For more information about the individual H2 blocker medications, please check out the resources below.

• Axid
• Pepcid
• Tagamet
• Zantac

<sub>Sources:

"Pharmacodynamic Aspects of Hz-Blockers versus proton Pump Inhibitors." U.S. Food and Drug Administration. 26 Apr 2007

"Understanding Some of the Medications Often Prescribed for GERD & Ulcers." Common GI Problems: Volume 1. American College of Gastroenterology. 26 Apr 2007

Kenneth R. DeVault M.D., F.A.C.G., and Donald O. Castell M.D., M.A.C.G., "Updated Guidelines for the Diagnosis and Treatment of Gastroesophageal Reflux Disease." doi: 10.1111/j.1572-0241.2005.41217.x. American College of Gastroenterology. 24 Apr 2007

"Effectiveness of Therapies for GERD" American College of Gastroenterology. 26 Apr 2007</sub>

Edited by Richard N. Fogoros, MD