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. All are available over the counter without a prescription. Most work equally as well. Side effects may vary from drug to drug.
- Famotidine (Pepcid AC, Pepcid Oral, Zantac 360)
- Cimetidine (Tagamet, Tagamet HB)
- Nizatidine Capsules (Axid AR, Axid Capsules, Nizatidine Capsules)
- Ranitidine (Zantac) has been removed from the US market due to concerns about safety
Taking Your H2 Blockers
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 2 weeks or more for acid reflux symptoms, make sure you see your health care provider about your symptoms.
If you have a peptic ulcer, your provider may prescribe H2 blockers along with 2 or 3 other medicines for up to 2 weeks.
If your provider prescribed these medicines for you:
- Take all of your medicines as your provider told you to. Try to take them at the same time each day.
- Do not stop taking your medicines without talking to your provider first. Follow up with your provider 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, headaches, and gynecomastia may occur.
- Nizatidine. Side effects are rare.
If you are breastfeeding or pregnant, talk to your provider before taking these medicines. If you have kidney problems, do not use famotidine without talking to your provider.
Tell your provider 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 provider if:
- You are having side effects from your medicine
- You are having other symptoms
- Your symptoms are not improving
Peptic ulcer disease - H2 blockers; PUD - H2 blockers; Gastroesophageal reflux - H2 blockers; GERD - H2 blockers
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Richter JE, Vaezi MF. Gastroesophageal reflux disease. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 46.
Waller DG. Dyspepsia, peptic ulcer disease, and gastroesophageal reflux disease. In: Waller DG, Sampson A, Hitchings A, eds. Medical Pharmacology and Therapeutics. 6th ed. Philadelphia, PA: Elsevier; 2022:chap 33.
Review Date 5/3/2023
Updated by: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.