Famotidine

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Famotidine is an H2 receptor antagonist (commonly known as an H2 blocker) prescribed to reduce stomach acid production for the treatment of gastro-oesophageal reflux disease (GORD), duodenal and gastric ulcers, erosive oesophagitis, and pathological hypersecretory conditions such as Zollinger-Ellison syndrome.

It works by blocking histamine H2 receptors on the parietal cells of the stomach, significantly reducing both basal and meal-stimulated acid secretion.

Famotidine is available as 20 mg and 40 mg tablets and is classified as a prescription-only medicine (POM) in the UK at therapeutic doses.

It is the most potent H2 receptor antagonist available on a milligram-for-milligram basis.

Acid-related disorders are extremely common in the United Kingdom.

GORD affects an estimated 10 to 20% of the adult population, causing symptoms such as heartburn, acid regurgitation, chest discomfort, and difficulty swallowing.

Peptic ulcer disease, though less common than in previous decades due to improved Helicobacter pylori eradication, still affects a significant number of people and can cause serious complications including bleeding, perforation, and gastric outlet obstruction.

Famotidine provides an effective and well-tolerated option for acid suppression, either as primary therapy or as an alternative or adjunct to proton pump inhibitors (PPIs).

This page provides a comprehensive clinical guide to famotidine, covering its mechanism of action, clinical applications, dosing, side effects, safety information, and how to obtain a prescription in the United Kingdom.

Important safety information about famotidine

Before reading further, note the following key safety points.

• Before starting famotidine for new dyspeptic symptoms, your prescriber should exclude gastric malignancy, particularly if you have alarm features (unintentional weight loss, difficulty swallowing, persistent vomiting, anaemia, or abdominal mass).
• The dose must be reduced in severe renal impairment (creatinine clearance below 30 mL/min) to avoid drug accumulation.
• Use the lowest effective dose for the shortest duration necessary, as advised by the MHRA for all acid-suppressing medicines.
• Report any suspected adverse reactions to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Understanding stomach acid and acid-related disorders

The stomach produces hydrochloric acid to aid digestion, activate pepsinogen into pepsin (a protein-digesting enzyme), and kill ingested bacteria.

Acid secretion is regulated by three main chemical pathways: histamine (via H2 receptors), acetylcholine (via muscarinic M3 receptors), and gastrin (via CCK-B receptors) on parietal cells.

All three pathways ultimately converge on the proton pump (H+/K+-ATPase), which secretes hydrogen ions into the stomach lumen.

When the balance between acid production and mucosal defence mechanisms is disrupted, acid-related conditions develop.

In GORD, the lower oesophageal sphincter relaxes inappropriately, allowing acid to reflux into the oesophagus and cause inflammation and symptoms.

In peptic ulcer disease, the gastric or duodenal mucosa is damaged, most commonly by Helicobacter pylori infection or NSAID use, and acid prevents healing.

In Zollinger-Ellison syndrome, a gastrin-secreting tumour drives excessive acid production. Famotidine addresses all these conditions by reducing the volume and acidity of gastric secretions.

How famotidine works: mechanism of action

Famotidine is a competitive, reversible antagonist of histamine at the H2 receptor on gastric parietal cells.

Histamine is released from enterochromaffin-like (ECL) cells in the gastric mucosa in response to gastrin and vagal stimulation.

When histamine binds to the H2 receptor, it activates adenylate cyclase, increasing intracellular cyclic AMP, which stimulates the proton pump to secrete acid.

By occupying the H2 receptor and preventing histamine binding, famotidine inhibits this signalling cascade.

Famotidine is the most potent H2 antagonist currently available.

On a weight-for-weight basis, it is approximately 20 to 50 times more potent than cimetidine and 3 to 20 times more potent than ranitidine (which was withdrawn from the UK market in 2020 due to NDMA contamination concerns).

A single 20 mg dose of famotidine inhibits basal gastric acid secretion by approximately 90% and meal-stimulated secretion by approximately 75%, with acid-suppressive effects lasting 10 to 12 hours.

The 40 mg dose provides more profound and prolonged suppression.

Unlike proton pump inhibitors, which irreversibly inactivate the H+/K+-ATPase enzyme, H2 blockers such as famotidine produce a competitive, reversible block.

This means that the degree of acid suppression can be overcome by very high levels of histamine or other secretagogues.

Consequently, PPIs generally provide more potent and sustained acid suppression than H2 blockers and are preferred for severe erosive oesophagitis and complicated ulcer disease.

However, famotidine retains an important clinical role in milder disease, as maintenance therapy, for nocturnal acid breakthrough, and in patients who prefer or tolerate H2 blockers better than PPIs.

Clinical applications of famotidine

Gastro-oesophageal reflux disease (GORD)

Famotidine is effective for the symptomatic treatment of mild to moderate GORD, providing relief from heartburn, acid regurgitation, and related symptoms.

NICE guideline NG12 recommends offering a 4-week course of a PPI or H2 receptor antagonist for uninvestigated dyspepsia with predominant reflux symptoms.

Famotidine is an appropriate choice for patients with mild symptoms, those who prefer an H2 blocker, or those who experience side effects with PPIs.

For patients with confirmed erosive oesophagitis, higher doses (40 mg twice daily) may be needed, though PPIs are generally more effective for healing oesophageal erosions.

Peptic ulcer disease

Famotidine accelerates the healing of duodenal and gastric ulcers by reducing intraluminal acid, creating a more favourable environment for mucosal repair.

For duodenal ulcers, 40 mg at bedtime heals approximately 90% of ulcers within 4 weeks and over 95% within 8 weeks.

For gastric ulcers, healing rates are slightly lower and a full 8-week course is usually required.

If Helicobacter pylori is present, eradication therapy (typically a PPI-based triple therapy) should be given concurrently.

After ulcer healing, maintenance famotidine 20 mg at bedtime can be used to prevent relapse in patients at high risk of recurrence.

Zollinger-Ellison syndrome

In this rare condition, a gastrin-secreting tumour causes massive acid hypersecretion.

Famotidine can be used at high doses (up to 800 mg daily in divided doses) to control acid output, although PPIs have largely replaced H2 blockers as the preferred medical management.

Famotidine may still be used as adjunctive therapy or in patients who do not tolerate PPIs.

Nocturnal acid breakthrough

Some patients on twice-daily PPI therapy experience a period of acid hypersecretion during the night ("nocturnal acid breakthrough").

Adding a bedtime dose of an H2 blocker such as famotidine 20 mg can suppress this nocturnal acid peak.

However, tolerance (tachyphylaxis) to H2 blockers may develop with regular nightly use, limiting long-term efficacy of this strategy.

UK prescribing guidelines and NICE recommendations

NICE guideline NG12 (Gastro-oesophageal reflux disease and dyspepsia in adults: investigation and management) recommends a trial of acid suppression for patients with uninvestigated dyspepsia after testing for and treating H.

pylori. Either a PPI or an H2 receptor antagonist may be used for 4 weeks.

If symptoms recur after initial treatment, the lowest effective dose of acid suppression should be used, stepping down from PPI to H2 blocker where possible.

NICE emphasises that acid-suppressing medicines should be used at the minimum effective dose for the minimum duration necessary.

The British National Formulary (BNF) lists famotidine under gastric acid secretion inhibitors and provides dosing for duodenal ulcer, gastric ulcer, GORD, and Zollinger-Ellison syndrome.

Famotidine became particularly important in the UK after ranitidine was withdrawn from the market in 2020 following detection of the impurity NDMA.

Famotidine has not been associated with NDMA contamination and has effectively replaced ranitidine in clinical practice.

Famotidine compared with other acid-suppressing medicines

Famotidine versus proton pump inhibitors

PPIs (omeprazole, lansoprazole, esomeprazole, pantoprazole, rabeprazole) are more potent acid suppressors than famotidine and are generally preferred for severe GORD, erosive oesophagitis, and Zollinger-Ellison syndrome.

However, famotidine offers several advantages in appropriate clinical settings.

Its onset of acid suppression is faster (1 to 3 hours versus 2 to 5 hours for PPIs), making it useful for on-demand symptom relief.

It has a lower drug interaction potential. It may be preferred in patients experiencing PPI-related side effects or in those seeking to step down from long-term PPI therapy.

NICE recommends considering a step-down from PPI to H2 blocker in patients whose symptoms are well controlled.

Famotidine versus ranitidine

Ranitidine was the most widely prescribed H2 blocker in the UK until its withdrawal in 2020 due to NDMA contamination.

Famotidine is more potent and has effectively replaced ranitidine in clinical practice. It has no association with NDMA contamination and has a comparable safety and tolerability profile.

Dosage and administration of famotidine

Famotidine tablets are taken with water. For ulcer treatment, the usual regimen is 40 mg once daily at bedtime for 4 to 8 weeks.

For GORD, the dose is typically 20 mg twice daily for 6 to 12 weeks, with the option of increasing to 40 mg twice daily for erosive oesophagitis.

For maintenance of ulcer healing, the dose is 20 mg once daily at bedtime.

For Zollinger-Ellison syndrome, the starting dose is 20 mg every 6 hours, adjusted according to acid output measurements.

In renal impairment (creatinine clearance below 30 mL/min), the dose should be halved or the interval doubled.

Famotidine can be taken with or without food.

The bedtime dose is preferred for ulcer treatment because nocturnal acid secretion is a major contributor to ulcer pathogenesis and nocturnal symptom burden.

If a dose is missed, take it as soon as you remember, unless it is close to the time of the next dose.

Side effects of famotidine

Common side effects

Headache, dizziness, constipation, and diarrhoea are the most frequently reported adverse effects, occurring in approximately 1 to 5% of patients. These are usually mild and transient. Dry mouth, nausea, and fatigue have also been reported occasionally.

Uncommon and rare side effects

CNS effects including confusion, hallucinations, agitation, and depression have been reported rarely and are more common in elderly patients or those with renal impairment.

These effects are reversible on dose reduction or discontinuation. Famotidine penetrates the blood-brain barrier to a lesser extent than cimetidine, making CNS effects less common.

Rare haematological effects include thrombocytopenia, leucopenia, and agranulocytosis. Rare hepatic effects include elevated transaminases and cholestatic jaundice. Hypersensitivity reactions including urticaria, angioedema, bronchospasm, and anaphylaxis have been reported very rarely.

Long-term considerations

Prolonged acid suppression may alter the gut microbiome, increase susceptibility to gastrointestinal infections (notably Clostridioides difficile), and reduce absorption of certain nutrients including vitamin B12, calcium, magnesium, and iron.

These concerns are more established for PPIs than for H2 blockers, but the MHRA advises caution with all acid-suppressing medicines used long term. Regular clinical review is recommended.

When to seek urgent medical advice

Contact your GP or NHS 111 if you experience persistent or severe headache, confusion, yellowing of the skin or eyes, dark urine, unusual bruising or bleeding, or significant changes in bowel habit.

Seek emergency care (call 999 or attend A&E) if you develop signs of a severe allergic reaction (swelling of face, lips, tongue, or throat, difficulty breathing), vomiting blood, or passing black tarry stools.

Report any suspected adverse reactions to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Excluding gastric malignancy

Acid suppression can mask the symptoms of gastric cancer.

Any patient presenting with new dyspeptic symptoms should be assessed for alarm features (unintentional weight loss, progressive dysphagia, persistent vomiting, gastrointestinal bleeding, iron deficiency anaemia, or an epigastric mass).

Patients with alarm features should be referred for urgent investigation, typically upper gastrointestinal endoscopy, before or alongside starting acid suppression.

Renal impairment

Famotidine is primarily excreted renally. In patients with severe renal impairment (creatinine clearance below 30 mL/min), the elimination half-life increases substantially.

The dose should be halved or the dosing interval doubled to prevent accumulation, which may increase the risk of adverse effects, particularly CNS symptoms.

Drug interactions

By raising gastric pH, famotidine may reduce the absorption of drugs requiring an acidic environment, including ketoconazole, itraconazole, posaconazole oral suspension, atazanavir, rilpivirine, and dasatinib.

Discuss timing or alternative strategies with your prescriber if these medicines are co-prescribed.

Famotidine has a much lower CYP450 interaction potential than cimetidine and does not significantly affect theophylline, warfarin, or diazepam metabolism at standard doses.

Pregnancy and breastfeeding

Famotidine crosses the placenta. It should be used during pregnancy only if the potential benefit outweighs the risk.

Animal studies have not demonstrated foetal harm, but adequate human data are lacking. Famotidine is excreted in breast milk.

Discuss the risks and benefits with your GP or midwife before use during breastfeeding.

Rebound acid hypersecretion

Prolonged use of H2 blockers may lead to upregulation of histamine receptors. Abrupt discontinuation can cause a temporary rebound increase in gastric acid secretion, potentially worsening symptoms.

If famotidine has been used continuously for more than a few weeks, your prescriber may recommend a gradual dose reduction rather than sudden cessation.

How to get famotidine in the UK

Famotidine 20 mg and 40 mg tablets are available on NHS prescription from your GP.

Famotidine 10 mg tablets are available over the counter from pharmacies as a pharmacy (P) medicine for the short-term relief of heartburn and indigestion in adults, without a prescription.

For ongoing treatment of ulcers, GORD, or other acid-related conditions, a prescription is required so that your GP can monitor your condition and adjust treatment as needed.

An authorised online prescriber registered with the GPhC can also prescribe famotidine following a clinical consultation.

The NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Lifestyle measures alongside famotidine

For GORD, lifestyle modifications complement medical treatment.

These include eating smaller, more frequent meals, avoiding eating within 2 to 3 hours of bedtime, raising the head of the bed by 10 to 20 cm, reducing intake of known trigger foods (fatty foods, spicy foods, citrus, chocolate, caffeine, alcohol, and carbonated drinks), losing weight if overweight, stopping smoking, and wearing loose-fitting clothing around the abdomen.

For peptic ulcer disease, avoiding NSAIDs (unless specifically prescribed with gastroprotection) and limiting alcohol intake support ulcer healing alongside famotidine treatment.

When to seek medical advice

Contact your GP or NHS 111 if your symptoms do not improve after 2 to 4 weeks of treatment, if symptoms worsen, or if new symptoms develop.

Attend scheduled review appointments so your GP can assess whether to continue, adjust, or step down your acid-suppressing therapy.

If you experience alarm features at any time (difficulty swallowing, unintentional weight loss, persistent vomiting, blood in vomit or stools, or unexplained anaemia), seek urgent medical assessment.

Report any suspected adverse reactions via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk .

Sources

• Famotidine 20 mg and 40 mg Tablets, Summary of Product Characteristics (EMC)
• Famotidine, British National Formulary (BNF)
• NICE CG184: Gastro-oesophageal reflux disease and dyspepsia in adults
• Heartburn and acid reflux, NHS
• Stomach ulcer, NHS
• MHRA Yellow Card Scheme