A histamine-2 receptor antagonist used for the treatment and prevention of duodenal and gastric ulcers, GERD, erosive esophagitis, and conditions involving pathological gastric acid hypersecretion. Famotidine provides effective acid suppression with a favorable drug interaction profile compared to cimetidine.
Treatment of pathological hypersecretory conditions
What to watch for
Headache
Dizziness
Constipation
Known hypersensitivity to famotidine or other H2 antagonists1,2
Severe renal impairment (dose adjustment required)
The bottom line
Evidence rating strong. Most-documented uses: relief of heartburn and acid indigestion, healing of duodenal ulcers, treatment of gerd symptoms. 10 sources indexed (1995–2025), with 4 interaction records on file.
The science
How it works, mechanistically.
Core mechanism
Competitively blocks histamine H2 receptors on the basolateral membrane of gastric parietal cells, inhibiting histamine-stimulated acid secretion. This reduces both basal and nocturnal acid output as well as acid secretion stimulated by food, pentagastrin, and other secretagogues.4
Class
H2 Receptor Antagonist
Dosing
Dosing & protocol.
Common range
20–40 mg once or twice daily (as prescribed by your physician)
Recommended form
Tablet or oral suspension; IV available
Can be taken with or without food; for heartburn prevention, take 15–60 minutes before eating trigger foods
Depletions
What it depletes.
Nutrients this medication can lower over time, and what to replace.
Vitamin B12
Mild
Chronic H2 receptor blockade reduces gastric acid needed to release food-bound vitamin B12 before intrinsic factor binding.
Replace MethylcobalaminMonitor Serum B12 + methylmalonic acidOnset Usually after months to years of continuous therapy
Safety
Full safety detail.
Side effects
Headache
Dizziness
Constipation
Diarrhea
Fatigue
Muscle cramps
Contraindications
Known hypersensitivity to famotidine or other H2 antagonists1,2
Severe renal impairment (dose adjustment required)
Caution in elderly patients (increased risk of confusion)
Long-term famotidine therapy can lower vitamin B12 status by reducing acid-pepsin-dependent release of B12 from food. The Kaiser case-control study found that two or more years of H2 blocker use was associated with a 25% higher risk of B12 deficiency. The effect is smaller than with PPIs but real, and matters more in older adults and vegetarians.
Recommendation: If you take famotidine daily for more than two years, ask for a periodic serum B12 check. A daily oral B12 supplement, ideally methylcobalamin, is a reasonable insurance step and does not require gastric acid for absorption.
Famotidine can reduce absorption of oral iron, especially non-heme iron salts that require gastric acid. In the Kaiser study, two or more years of H2 blocker use was associated with about a 1.6-fold increase in iron deficiency risk. The effect is smaller than with PPIs but still clinically relevant in patients with menstrual or GI losses.
Recommendation: Take iron supplements at least 2-4 hours apart from famotidine. Iron bisglycinate or a heme-iron product is less acid-dependent. Recheck ferritin 3 months after starting iron repletion.
Famotidine reduces gastric acid and can lower the absorption of calcium carbonate, which depends on acid to dissolve. The fracture-risk signal is weaker for H2 blockers than for PPIs, but the absorption effect is plausible and worth noting for patients who use calcium carbonate as their primary calcium source.
Recommendation: If you take famotidine regularly, prefer calcium citrate, which absorbs well without gastric acid. If using calcium carbonate, take it with a meal when residual acid is highest.
Methylcobalamin (a free coenzyme form of B12) does not require gastric acid for absorption, making it a reliable supplemental B12 source for patients on famotidine. Two or more years of H2 blocker use is associated with a 25% higher B12 deficiency risk, which oral methylcobalamin can prevent in most patients.
Recommendation: If you take famotidine long-term, 500-1000 mcg of oral methylcobalamin daily is a sensible insurance dose. Ask for an annual serum B12 check while on chronic famotidine.
Poynard T, Lemaire M, Agostini H. Meta-analysis of randomized clinical trials comparing lansoprazole with ranitidine or famotidine in the treatment of acute duodenal ulcer. European journal of gastroenterology & hepatology. 1995
Amini M, Ghamar Chehreh ME, Khedmat H et al.. Famotidine in the treatment of functional dyspepsia: a randomized double-blind, placebo-controlled trial. The Journal of the Egyptian Public Health Association. 2012
Kawano S, Murata H, Tsuji S et al.. Randomized comparative study of omeprazole and famotidine in reflux esophagitis. Journal of gastroenterology and hepatology. 2002
Zhang D, Cai Y, Sun Y et al.. A Real-World Disproportionality Analysis of Histamine H2-Receptors Antagonists (Famotidine): A Pharmacovigilance Study Based on Spontaneous Reports in the FDA Adverse Event Reporting System. Drug development research. 2025
Bello AE, Kent JD, Holt RJ. Gastroprotective efficacy and safety of single-tablet ibuprofen/famotidine vs ibuprofen in older persons. The Physician and sportsmedicine. 2015
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