H2 blockers are medicines that work by reducing the amount of stomach acid secreted by glands in the lining of your stomach.
How H2 Blockers Help You
H2 blockers are used to:
Relieve symptoms of acid reflux, or gastroesophageal reflux disease (GERD), a condition where food or liquid travels backwards from the stomach to the esophagus (the tube from the mouth to the stomach)
Treat a peptic or stomach ulcer
Types of H2 Blockers
There are many different names and brands of H2 blockers. Most work as well as another. Side effects may be different for different ones.
H2 blockers are most often taken by mouth and are found as tablets, liquids, or capsules.
The most common way of taking them is with the first meal of the day.
It takes 30 - 90 minutes for them to work, but the benefits last for hours. People often take the drugs at bedtime too.
Symptoms may improve for up to 24 hours after taking the drug.
H2 blockers may be bought in lower doses at the store without a prescription. If you find yourself taking these most days for acid reflux symptoms for 2 weeks or more, make sure you see your health care provider about your symptoms.
If you have a peptic ulcer, your doctor may prescribe H2 blockers along with two or three other medicines for up to 2 weeks.
If your doctor prescribed these medicines for you:
Take all of your medicines as your doctor told you to. Try to take them at the same time, or times, each day.
Do not stop taking your medicines without talking with your doctor first. Follow up with your doctor regularly.
Plan ahead so that you do not run out of medicine. Make sure you have enough with you when you travel.
Side effects from H2 blockers are rare.
Famotidine: most common side effect is headache
Cimetidine: side effects are rare at diarrhea, dizziness, rashes, or headaches may occur
Ranitidine: most common side effect is headache
Nizatidine: side effects are rare
If you are breastfeeding or pregnant, talk to your health care provider before taking these medications. Anyone with kidney problems should use famotidine only under a doctor's direction.
Tell your health care provider if you are also taking other medicines. H2 blockers may change the way certain drugs work. Cimetidine and nizatidine are least likely to have this problem.
When to Call the Doctor
Call your doctor if you are having any of the side effects above. Also call your doctor if you are having other unusual symptoms or your symptoms are not improving.
Kahrilas PJ, Shaheen NJ, Vaezi MF, Hiltz SW, Black E, Modlin IM. American Gastroenterological Association Medical Position Statement on the management of gastroesophageal reflux disease. Gastroenterology. 2008;135:1383-1391.
Richter JE, Friedenberg FK. Gastroesophageal reflux disease. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 43.
George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.