H2-histamine receptor antagonist
ATC code: A02BA03 (Famotidine)
Brand names
Pepcid, Pepcid AC, Famox, Tamin
A competitive reversible antagonist of H2 histamine receptors on gastric parietal cells. Reduces basal and food-stimulated hydrochloric acid secretion by 70–90% for 10–12 hours. Compared with other H2-blockers (cimetidine, ranitidine), more selective and does not inhibit CYP enzymes – fewer drug interactions. After ranitidine's 2020 worldwide withdrawal due to N-nitrosodimethylamine (NDMA) contamination, it is the only widely available H2-blocker.
Second line
Alternative to proton pump inhibitors in mild-to-moderate GERD when PPIs are intolerable, or for nocturnal acid breakthrough as PPI add-on. Dose 20–40 mg twice daily. Less effective than PPIs – omeprazole and suppress acid 80–95% over 24 hours versus 70% with famotidine. Used for episodic symptoms or nocturnal acidity.
Second line
Used in gastric and duodenal ulcer when PPIs are intolerable, or as maintenance after ulcer healing. Dose 40 mg once daily at bedtime for 4–8 weeks. 2017 sets PPIs plus H. pylori eradication as first-line; H2-blockers remain an alternative.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Famotidine is an H2-receptor antagonist. It is prescribed for gastric and duodenal peptic ulcer, GERD, and stress ulcer prophylaxis (AEMPS Ficha Técnica). In alt detox circles, famotidine is occasionally promoted for stomach protection in healthy people without a confirmed diagnosis. In people without peptic ulcer disease or GERD, no clinical studies of prophylactic use exist. The drug is relatively safe but on long-term use can cause vitamin B12 deficiency (via reduced gastric acidity), decreased calcium and iron absorption, and confusion in older adults. If famotidine is being taken for detox or stomach protection without confirmed diagnosis, consider seeking a second opinion.
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FDA category B. Use in pregnancy is acceptable when indicated. Large pregnancy data set without described teratogenic effects.
Compatible with breastfeeding. Milk concentrations are low.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Famotidine is evaluated for the following indications with varying evidence strength: Peptic ulcer disease (evidence tier B), Gastroesophageal reflux disease (evidence tier B), Body detoxification and cleansing (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Famotidine (≥ 1 in 100): Headache, Dizziness, Constipation or diarrhea, Dry mouth. See the Safety section for uncommon and serious reactions.
FDA category B. FDA category B. Use in pregnancy is acceptable when indicated. Large pregnancy data set without described teratogenic effects.
Compatible with breastfeeding. Milk concentrations are low.
Famotidine is contraindicated in: Famotidine or other H2-blocker hypersensitivity; Severe renal impairment without dose adjustment. Full list in the Safety section.