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). This is a condition where food or liquid moves up from the stomach into the esophagus (the tube from the mouth to the stomach).
Treat a peptic or stomach ulcer.
Types of H2 blockers
There are different names and brands of H2 blockers. Most work equally as well. Side effects may vary from drug to drug.
H2 blockers are most often taken by mouth. You can get them in the form of tablets, liquids, or capsules.
These medicines are most often taken with the first meal of the day. In some cases, you may also take them before your evening meal.
It takes 30 to 90 minutes for the medicines to work. The benefits will last several hours. People often take the drugs at bedtime, as well.
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 doctor 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 each day.
Do not stop taking your medicines without talking to 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. The most common side effect is headache.
Cimetidine. Side effects are rare. But diarrhea, dizziness, rashes, or headaches may occur.
Ranitidine. The most common side effect is headache.
Nizatidine. Side effects are rare.
If you are breastfeeding or pregnant, talk to your doctor before taking these medicines. If you have kidney problems, do not use famotidine without talking to your doctor
Tell your doctor about other medicines you are taking. H2 blockers may change the way certain drugs work. This problem is less likely with cimetidine and nizatidine.
When to call the doctor
Call your doctor if:
You are having side effects from your medicine
You are having other symptoms
Your symptoms are not improving
Katz PO, Gerson LB, Vela MF. Guidelines for the diagnosis and management of gastroesophageal reflux disease. Am J Gastroenterol. 2013;108:308-328.
Richter JE, Friedenberg FK. Gastroesophageal reflux disease. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger & 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, Bethanne Black, and the A.D.A.M. Editorial team.