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An H2 blocker is a medicine that reduces stomach acid by blocking histamine-2 receptors in the stomach lining. H2 blockers are also called H2 receptor antagonists. They are used for heartburn, acid reflux, GERD, and some ulcer-related conditions. Some H2 blockers are sold over the counter, while others require a prescription.
read more about h2 blocker ...Histamine can attach to H2 receptors on stomach acid-producing cells. When that happens, the stomach releases more acid. H2 blockers reduce this signal, so less acid is secreted. They do not neutralize acid already in the stomach the way antacids do.
H2 blockers are used for occasional heartburn, acid indigestion, gastroesophageal reflux disease, and certain ulcers. They can be taken before symptoms occur or after symptoms begin, depending on the product and clinician's directions. They can also be used at bedtime when nighttime acid symptoms are a problem. Frequent or severe symptoms should be checked by a clinician.
Common H2 blockers include famotidine, cimetidine, and nizatidine. Famotidine is widely used for heartburn and acid reflux symptoms. Cimetidine can interact with several medicines because it affects certain liver enzymes. H2 blockers are different from proton pump inhibitors, which block acid pumps more directly and can reduce acid more strongly.
H2 blockers can cause headache, dizziness, diarrhea, constipation, nausea, or tiredness. Confusion can occur in susceptible patients, especially older adults or people with kidney problems. Cimetidine can have more drug interactions than some other H2 blockers. Seek care for chest pain, trouble swallowing, vomiting blood, black stools, severe allergic reaction, or heartburn that keeps returning.
Yes, famotidine is an H2 blocker. It reduces stomach acid by blocking histamine-2 receptors in the stomach lining.
No, H2 blockers and PPIs both reduce stomach acid, but they work through different mechanisms. PPIs usually reduce acid more strongly and for longer.
H2 blockers can start working sooner for some people, while PPIs can give stronger acid control over time. The better option depends on symptoms and diagnosis.
Yes, some H2 blockers can interact with other medicines. Cimetidine has more interaction concerns than famotidine, so a pharmacist can help check safety.
H2 Blockers: What They Are, Conditions Treated. Cleveland Clinic. https://my.clevelandclinic.org/health/articles/h2-blockers. Date Accessed June 3, 2026.
H2 Blockers. StatPearls (NCBI Bookshelf). https://www.ncbi.nlm.nih.gov/books/NBK525994/. Date Accessed June 3, 2026.
Famotidine: MedlinePlus Drug Information. MedlinePlus. https://medlineplus.gov/druginfo/meds/a687011.html. Date Accessed June 3, 2026.
Cimetidine: MedlinePlus Drug Information. MedlinePlus. https://medlineplus.gov/druginfo/meds/a682256.html. Date Accessed June 3, 2026.
Famotidine (oral route). Mayo Clinic. https://www.mayoclinic.org/drugs-supplements/famotidine-oral-route/description/drg-20072972. Date Accessed June 3, 2026.