Gastroenterology: Medications

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H2 Blockers [Tagamet, Zantac, Axid, Pepcid ]

Many people are not as well-informed about their prescription medicine as they ought to be. We believe the more you know about your medications the better. This is an attempt to inform you about a group of medications that we frequently prescribe for the treatment of peptic ulcer disease and other acid-related disorders.

If any of this information causes you concern or if you desire additional information about these medicines and their use, please check with your doctor, or pharmacist.

Remember always to keep the medication, along with all prescription drugs, beyond the sight and reach of children when not in use, and to store them in their original labeled container in a cool, dry location. Always read the instructions on the label carefully before each use.

What are H2 Blockers?

H2 blockers are a class of medications also known as histamine blockers, which block the action of histamine and thus inhibit the secretion of stomach acid creating a more favorable environment for the treatment of peptic ulcer disease, gastritis and severe heartburn. Although these medicines are classified as histamine blockers, their major action occurs against the histamine in the stomach and not in the skin or the sinuses. Thus these medications differ somewhat from commonly prescribed antihistamines.

The following is a list of H2 blockers available in both brand and generic names:

Brand Name

Generic Name

Rx Strength

OTC Name

OTC Strength
Tagamet Cimetidine 200 mg. 300 mg. 400 mg. 800 mg. Tagamet HB 200 mg.
Zantac Ranitidine 150 mg 300 mg. Tagamet 75 75 mg.
Pepcid Famotidine 20 mg. 40 mg. Pepcid AC 10 mg.
Axid Nizatidine 150 mg. 300 mg. Axid AR 75 mg.

These medicines do not neutralize stomach acid like Maalox, or other liquid antacids, instead they work by preventing the formation of acid. The chemical histamine plays a key role in the normal production of stomach acid. Tagamet was the first of a class of drugs in 1976 called histamine blockers, other similar drugs are Zantac (Ranitidine), Pepcid (Famotidine), and Axid (Nizatidine).

Taking H2 Blockers properly

1. Take the dose as prescribed. Initially, your doctor will determine what dose is best for you depending on the activity of your disease, your age, your weight, and any other medical conditions you may have. Do not alter the dose on your own. Your doctor will routinely reassess what dose is necessary for you. The goal, of course, is to control your illness with the lowest effective dose possible.

2. H2 blockers can be taken either on an empty stomach or with food or milk. They are usually prescribed once or twice daily. If taken only once a day, it is best to take the medication at bedtime. The tablets can be chewed or crushed if necessary. There are no food or beverage restrictions due to H2 blockers.

3. Do not miss doses. However, if you do miss a dose, take your normal dose, skip the missed dose, and go back to your regular schedule. While an occasional unintentional extra dose is unlikely to be harmful, do not double doses.

4. Do not stop taking this medication on your own. If you have a peptic ulcer, you should take the full course of treatment as prescribed by your doctor. Keep taking the H2 blockers even if your symptoms quickly disappear. The painful symptoms of an ulcer can improve on H2 blockers even before the ulcer is completely healed. The usual duration of therapy to heal a peptic ulcer ranges from 4 to 8 weeks.

5. H2 blockers can also be taken for long-term. H2 blockers are not only prescribed for short-term treatment, but are also often given as long-term "maintenance" treatment to help prevent the return of an ulcer, reduce excessive stomach acid, and in the treatment of reflux esophagitis, severe heartburn and hiatal hernia.

6. Over-the-counter preparations. Since the release of H2 blockers, there has been a proliferation of over-the-counter preparations with the same name that are easily available. It should be noted that these preparations are of suboptimal dose for treating peptic ulcer disease and are recommended mostly for occasional indigestion or heartburn. These are not to be substituted for prescription strength histamine blockers and should only be used short-term for mild symptoms. If symptoms persist, you should really talk to a physician about getting evaluated for acid peptic disease.

7. Dosages. There are various dosages of all of the H2 blockers and from 6 to 8 weeks all of the H2 blockers will heal over 90% of peptic ulcer disease. However, in the case of heartburn or severe gastroesophageal reflux disease, occasionally patients will have to stay on H2 blockers indefinitely and even at a higher dose. Please check with your physician or pharmacist if you have any questions.

What are the side effects?

All medicines - even those purchased without a prescription - may sometimes produce unwanted side effects. In general, the risk of significant side effects from H2 blockers is quite low. You can help limit possible side effects by taking the medications exactly as prescribed and reporting any problems to your doctor. It is important that you keep all your appointments with your doctor so that he can be sure the medication is working and check for possible side effects.

These side effects should be reported to your doctor:

  • Severe skin rash, severe itching
  • Unexplained fever
  • Severe headaches
  • Enlarged or painful breasts
  • Hallucinations, confusion
  • Impotence

The following side effects usually do not require medical attention. They often will go away as our body becomes used to the medication. However, if they continue or are bothersome, check with your doctor:

  • Mild headache
  • Dizziness
  • Diarrhea
  • Muscle cramps or pain
  • Tiredness or weakness.

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor, nurse, or pharmacist.


It is safe to take antacids as needed while taking H2 blockers, but do not take antacids at the same time as your dose of H2 blocker. Antacids can decrease absorption of this drug. If you need antacids, take them at least 2 hours before or after your H2 blocker. Cigarette smoking will block the beneficial effects of H2 blockers. You should not smoke or chew tobacco when taking these drugs.

Some H2 blockers interact with many other types of medications. Be sure to notify your doctor if you are currently taking any medications especially:


Inform your doctor if you are pregnant, planning to become pregnant soon, or breast-feeding. We feel it is best to avoid all potent prescription drugs during pregnancy whenever possible.

While H2 blockers are effective in healing peptic ulcers and treating reflux esophagitis, they do not exert any long-term protective action once the medication has been discontinued. Be alert to the possibility of ulcer recurrence anytime after stopping the drug. If you suspect that your problem has returned, contact your doctor.


H2 blockers are powerful drugs with many helpful properties, but as with all medications, side effects may occur. You can best limit problems with these medications by taking them exactly as prescribed. If you have any questions or concerns, please discuss them with your doctor.

Text & Images Courtesy of Three Rivers Endoscopy Center
© Dr. Robert Fusco, Three Rivers Endoscopy Center, All Rights Reserved

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