Famotidine

Famotidine is used across multiple products and formulations to treat a wide range of acid-related conditions.

• Over-the-counter tablets (including Acid Controller, Acid Reducer, Acid Relief, Amazon Basic Care Acid Reducer, basic care acid reducer, and Calmicid AC): relieve and prevent heartburn associated with acid indigestion and sour stomach
• Prescription famotidine tablets (adults and pediatric patients weighing 40 kg or more): active duodenal ulcer, active gastric ulcer, symptomatic nonerosive GERD, and erosive esophagitis due to GERD
• Prescription famotidine tablets (adults only): pathological hypersecretory conditions such as Zollinger-Ellison syndrome and multiple endocrine neoplasias; reduction of the risk of duodenal ulcer recurrence
• Famotidine oral suspension (adults): active duodenal ulcer, active gastric ulcer, GERD, erosive esophagitis due to GERD, pathological hypersecretory conditions, and reduction of risk of duodenal ulcer recurrence
• Famotidine oral suspension (children 1 year and older): peptic ulcer disease and GERD with or without esophagitis and ulcerations
• Famotidine oral suspension (infants from birth to less than 1 year): GERD
• Famotidine injection (intravenous, hospitalized patients): short-term treatment of active duodenal ulcer, active benign gastric ulcer, pathological hypersecretory conditions, and as an alternative for patients unable to take oral medication

Famotidine is a competitive H2-receptor antagonist (blocker). Histamine-2 receptors in the stomach lining respond to signals that trigger acid production. Famotidine occupies and blocks those receptors, reducing both the amount and concentration of acid the stomach produces. Less acid means less irritation — allowing ulcers to heal and reducing the burning and discomfort of GERD and heartburn.

Importantly, famotidine does not appear to affect hormone levels (including prolactin, testosterone, and cortisol), and has no meaningful effect on gastric emptying or the pancreas.

How famotidine is taken depends on the product, the condition, and the patient.

• OTC tablets (Acid Reducer, Acid Controller, Acid Relief, etc.): swallowed whole with water, with or without food — either to relieve symptoms as they occur, or taken 10–60 minutes before trigger foods or drinks to prevent heartburn; no more than 2 tablets in 24 hours; not for use beyond 14 days without a doctor's guidance
• Prescription tablets and oral suspension: typically taken once or twice daily, with or without food — once daily before bedtime or twice daily in the morning and before bedtime; the exact schedule depends on the condition; follow your prescriber's instructions precisely
• Famotidine injection: given intravenously in a hospital setting only, for patients who cannot take oral medication
• Patients with moderate or severe kidney impairment may need lower doses or adjusted timing — always follow your prescriber or pharmacist's specific guidance

Famotidine is generally well tolerated. The most commonly reported side effects include:

• Headache
• Dizziness
• Constipation
• Diarrhea
• Nausea or vomiting
• Abdominal discomfort
• Dry mouth
• Fatigue or weakness

More serious reactions have been reported after marketing, including severe allergic reactions (anaphylaxis, swelling, hives), heart rhythm problems (arrhythmia, QT prolongation), liver inflammation, serious skin reactions (Stevens-Johnson syndrome/toxic epidermal necrolysis), and rare blood cell count changes. CNS reactions — including confusion, hallucinations, agitation, and seizures — have been reported mainly in elderly patients and those with kidney impairment. Contact your doctor or seek emergency care right away if any of these occur.

• CNS side effects in vulnerable patients: Confusion, delirium, hallucinations, agitation, seizures, and lethargy have been reported in elderly patients and those with moderate or severe kidney impairment. Famotidine is cleared by the kidneys, so levels can build up in patients with reduced kidney function. Dose reduction is recommended in these groups.
• Heart rhythm (QT prolongation): Abnormal heart rhythms, including prolonged QT interval (a change in the heart's electrical activity that can cause dangerous arrhythmias), have been reported in patients with moderate or severe kidney impairment.
• Gastric malignancy: In adults, improvement in symptoms does not rule out stomach cancer. If you don't respond to treatment or symptoms return quickly after finishing a course, your doctor should evaluate you further.
• OTC warning signs requiring a doctor visit: Do not use OTC famotidine if you have trouble swallowing, vomiting with blood, or bloody or black stools. Stop use if heartburn continues or worsens, or if you need the product for more than 14 days.
• Allergic reactions: Do not use famotidine if you have had a serious allergic reaction to famotidine or any other H2 blocker.

Famotidine can interact with several drugs, mainly because it lowers stomach acid levels — which affects how some medications are absorbed.

• Dasatinib, delavirdine mesylate, cefditoren, fosamprenavir: Co-administration is not recommended — famotidine can significantly reduce absorption of these drugs, making them less effective
• Atazanavir, erlotinib, ketoconazole, itraconazole, nilotinib, rilpivirine, ledipasvir/sofosbuvir: Famotidine may reduce their absorption; check the prescribing information for each drug for specific timing guidance
• Tizanidine (a muscle relaxant): Famotidine may raise tizanidine blood levels substantially, increasing the risk of dangerously low blood pressure, slow heart rate, or extreme drowsiness — avoid combining if possible; if necessary, monitor closely
• Other prescription drugs: Ask your doctor or pharmacist before combining famotidine with any prescription medication, as acid reducers can interact with a range of drugs

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not take famotidine if you have ever had a serious allergic reaction (anaphylaxis) to famotidine or any other H2 blocker
• Tell your doctor if you have kidney disease — famotidine accumulates when kidneys are not working well, increasing the risk of CNS and heart rhythm side effects
• Older adults should use the lowest effective dose and have kidney function monitored, as they are more vulnerable to CNS side effects
• Pregnant individuals: data on famotidine during pregnancy is limited; use only if clearly needed and under the guidance of a healthcare provider
• Breastfeeding individuals: consult a healthcare professional before use
• Children under 12 years: do not use OTC famotidine products without asking a doctor first
• Tell your doctor if you have had heartburn for more than 3 months, unexplained weight loss, frequent wheezing, chest pain, nausea, or stomach pain — these may indicate a more serious condition requiring evaluation before starting famotidine
• Adults who respond poorly to famotidine or relapse quickly after treatment should be evaluated for gastric malignancy (stomach cancer)

Taking too much famotidine tends to produce side effects similar to those seen at normal doses. In the event of an overdose, treatment is supportive — removing any unabsorbed medication and monitoring the patient. If you suspect an overdose, get medical help or contact a Poison Control Center right away at 1-800-222-1222.

After an oral dose, famotidine begins reducing stomach acid within about one hour, with the strongest effect occurring within one to three hours. A single evening dose suppresses nighttime acid secretion for at least 10 hours, and morning doses reduce food-triggered acid production throughout the day. The effect does not accumulate with repeated doses — each dose works independently. Famotidine does not meaningfully affect hormone levels, gastric emptying, or pancreatic function.

Famotidine taken by mouth is incompletely absorbed, with about 40–45% of a dose reaching the bloodstream. Peak blood levels occur within one to three hours of an oral dose. After an IV dose, the maximum effect is achieved within 30 minutes. The drug has an elimination half-life of 2.5 to 3.5 hours in adults with normal kidney function, but this can extend beyond 20 hours in patients with severe kidney impairment — which is why dose adjustments are necessary in those patients. Famotidine is cleared mainly through the kidneys (65–70%), with the remainder metabolized by the liver; only a small amount is converted to an inactive metabolite.

Store famotidine for oral suspension dry powder and constituted suspension at 25°C (77°F); excursions permitted to 15° to 30°C (59° to 86°F) . Protect from freezing. Dispense in a USP tight, light-resistant container.