Famotidine (Pepcid, Fluxid, Duexis): Uses, Dosage, Side effects, and Abuses
February 02, 201902,005

What is Famotidine?

Famotidine is a histamine H2-receptor blocker. It is used to decrease the amount of acid the stomach produces.1

It is sold under the brand name Pepcid and various generic names.1

You may buy famotidine in combination with ibuprofen as part of the drug Duexis.2

Famotidine used to be sold under the name Fluxid. This drug has been discontinued.3


How does famotidine work?

When we eat a meal, our stomachs make acid to help digest and sterilize our food.

Some of the key players in helping our stomachs make acid are enterochromaffin-like (ECL) cells.

ECL cells start producing a molecule called histamine when food enters the stomach.4

Histamine can bind to receptors (H2 histamine receptors) on other cells in the stomach that can produce acid. Histamine tells them it is time to start making acid.4

Famotidine stops acid production by preventing histamine from binding to its receptor on these cells. It does this by binding to the receptor instead.1,4

Famotidine sits in the way and histamine cannot bind. This prevents the acid-producing cells from being activated and making acid.1,4


Figure 1: Activation of acid-producing cells in the stomach.

ECL cells release histamine (pink circles) which bind to H2-receptors. Activated H2-receptors cause the H-K-ATPase to pump more acid into the stomach.
Famotidine prevents histamine from binding to the H2-recpetor (red line). Original diagram.


Famotidine Uses

The FDA has approved famotidine for1:

  • preventing and treating diseases caused by excess stomach acid
  • preventing and treating diseases made worse by excess stomach acid

Diseases caused by or made worse by excess stomach acid:

Stomach or Intestinal Ulcers

Stomach and intestinal ulcers are “holes” in the wall of the stomach or intestine.5,6

Stomach acid can create these holes if it comes into direct contact with the wall of the stomach or intestine. Normally, the walls of these organs are protected by a layer of mucus. If this layer breaks down and stomach acid gets through, it can eat away at the tissue and create an ulcer.5,6

Figure 2: Normal stomach wall compared to a stomach wall with an ulcer.

(modified from iStockphoto/elenabs)


The trigger for most ulcers in an infection with a bacterium called H. pylori. Unfortunately, treating the infection with antibiotics is not enough to heal the ulcer.5,6

It is necessary to protect the ulcer from harmful acid with famotidine or a similar drug. Only then can an ulcer heal well.1,5,6


Acid Reflux (GERD)

Acid reflux occurs when stomach acid gets into the throat (esophagus).7

Since stomach acid is not supposed to be in the throat, the throat does not have a protective lining. Stomach acid in the throat causes an immediate burning pain. It is often referred to as heartburn.7

Over time, pain can progress to inflammation and ulcers in the throat.7

Famotidine can help treat acid reflux by decreasing the amount of acid in the stomach. This decreases the amount of acid that can get into the throat.1

This not only treats heartburn symptoms, it also protects the throat from damage.1,7

If damage was already done, decreasing acid levels can give the throat a chance to heal.1,7


Zollinger-Ellison Syndrome

Zollinger-Ellison Syndrome (ZES) is a condition which causes benign tumors to grow in the pancreas.8

Sometimes these tumors can cause the pancreas to make extra hormones. Some of these hormones may make the stomach to produce too much acid.8

The treatment of this disorder is the removal of the tumor(s) from the pancreas.8

However, doctors often prescribe drugs like famotidine to protect the digestive tract from ulcers while preparations are made to treat the tumor(s).8

In some cases, a tumor cannot be removed or has become cancerous. These cases may require long-term therapy with famotidine.8


Multiple Endocrine Neoplasia-1

Multiple Endocrine Neoplasia-1 (MEN-1) is a genetic disorder that causes tumors to grow in the pituitary gland, parathyroid gland and pancreas.8

Unlike ZES, MEN-1 tumors are difficult to treat. Treatment for this disorder is often focused on managing the symptoms.8

If the tumors are making hormones that increase the amount of stomach acid being made, treatment may include famotidine to protect the digestive tract.8


Non-FDA Approved Uses of Famotidine

H2-receptors are not only found in the stomach.9

Histamine activation of H2-receptors in other parts of the body helps control9:

  • blood pressure
  • blood vessel function
  • mucus production

Over-activation of H2-receptors is believed to be involved in allergic reactions.9

For this reason, doctors sometimes give famotidine during severe allergic reactions.9

Though helpful in theory, there are no clinical studies proving that famotidine is effective in treating allergic reactions.9

For this reason, the FDA has not approved famotidine for the treatment of allergic reactions.1


Famotidine Dosage

The amount of famotidine your doctor prescribes will depend on1:

  • your age
  • the condition being treated
  • how bad your symptoms are
  • the way you will be taking the drug

Oral Dosages

Famotidine may be taken orally as a pill or a liquid. The dosage remains the same in both cases.1

You should take single daily doses of famotidine before bed. Your doctor will tell you how to space out multiple doses.1

Stomach Ulcer

For the treatment of a stomach ulcer, doctors usually prescribe 40 mg of famotidine once per day. Therapy usually lasts 4-8 weeks.1

Intestinal Ulcer

Intestinal ulcers are usually treated with 40 mg of famotidine per day. Your doctor may ask you to take one 40 mg dose or two 20 mg doses.1

Therapy may last 4-8 weeks.1

Once your ulcer has healed, your doctor may prescribe a follow-up therapy with famotidine. This helps prevent new ulcers from forming.

Dosage for the prevention of new ulcers is often 20 mg per day.1

Acid Reflux

The dose of famotidine commonly used to treat acid reflux is 20 mg twice per day.1

Therapy may last up to 6 weeks.1

If there is damage to your throat, your doctor may increase the dosage to 40 mg twice per day. She may also extend the length of your therapy to up to 12 weeks.1

ZES or MEN-1

Your doctor will tailor the dosage of famotidine to treat ZES or MEN-1 specifically to you.1

Your doctor is likely to start you off with 20 mg of famotidine every 6 hours. If your symptoms do not improve, she will increase your dosage until they do.1

The maximum dose of famotidine doctors have prescribed for ZES or MEN-1 is 160 mg every 6 hours.1


Child Oral Dosage: 1-16 years of age

Stomach ulcer

To treat a stomach ulcer, kids between the ages of 1 and 16 years may be given either1:

  • 5 mg of famotidine per kilogram of body weight, once per day


  • 25 mg of famotidine per kilogram of body weight, twice per day

The dosage may be increased up to a total of 2 mg/kg of body weight per day.1

Acid Reflux

If a child is diagnosed with acid reflux, their doctor may prescribe 0.5 mg/kg of body weight per day.

If the child’s throat shows damage, their doctor may increase the dose to 1.0 mg/kg of body weight. This may be given in one dose or divided into two doses of 0.5 mg/kg of body weight.1

The maximum total oral dosage of famotidine for children is 40 mg per day.1


Child Oral Dosage: 3 months-1 year of age

Acid Reflux

Children between 3 months and 1 year of age may be given famotidine to treat acid reflux.

Commonly, kids in this age group are given 0.5 mg/kg of body weight, twice per day.

Therapy may last up to 3 months.1


Child Oral Dosage: under 3 months of age

Acid Reflux

Infants under 3 months of age may be given famotidine for acid reflux.

The normal dosage for infants is 0.5 mg per kg of body weight per day.

Therapy may last up to 3 months.1


Injection Dosages

Famotidine may be given as a shot if you cannot swallow.1

Adults may be given up to 20 mg every 12 hours.1

Kids between the ages of 1 and 16 years may be given 0.25 mg/kg every 12 hours.1

Doctors do not recommend injecting famotidine into children under the age of 1 year.1


Famotidine Side Effects

Common Side Effects

The most common side effects of famotidine are1:

  • Headache
  • Dizziness
  • Constipation
  • Diarrhea

Famotidine may also cause1:

  • Ringing in the ears
  • Change in taste of food
  • Dry mouth
  • Loss of appetite
  • Dry skin
  • Red eyes
  • Acne
  • Joint or muscle pain
  • Tingling feeling in hands, feet, legs or arms
  • Fatigue
  • Fussiness and spitting up in small children


Serious Side Effects

Rarely, famotidine may cause more serious side effects. These include1:

  • Insomnia
  • Depression
  • Anxiety
  • Loss of sex drive
  • Growth of breast tissue (in men)
  • Confusion or delirium
  • Seizures
  • Pneumonia
  • Fever
  • Abnormal heart beat
  • Abnormal liver function
  • Jaundice
  • Low white blood cell counts (with risk of infection)
  • Anemia
  • Low platelet counts (with risk of bleeding)
  • Swelling of hands, feet, face or throat
  • Skin loss
  • Rash
  • Severe allergic reactions

Studies have also found that taking famotidine can increase your risk of infection with the bacterium clostridium difficile.10 C. difficile lives in the intestines. It can cause abdominal pain, diarrhea (sometimes bloody), fever and decreased white blood cell count.11

  1. difficile is often antibiotic resistant. An infection with C. difficile may become life-threatening.11

Long-term Side Effects

Studies have linked the use of histamine H2-receptor inhibitors for longer than 2 years to an increased risk of12,13:

  • Vitamin B12 deficiency
  • Osteoporosis
  • Bone fracture

Scientists think this is because stomach acid helps the body absorb vitamin B12 and minerals out of our food.12,13

If you need to take famotidine long-term, you should ask your doctor about ways to keep your B12 and bone mineral levels high.

Famotidine Overdose

No specific symptoms signify an overdose with famotidine. Overdose symptoms appear as an increase in the intensity or number of “normal” side effects.1

A fatal overdose with famotidine is unlikely, especially when taken orally.1

Animal studies suggest it would take an oral dose of hundreds of thousands of milligrams to cause fatal symptoms in an adult human.11


Warnings for Famotidine

General Warnings

You should not take famotidine if you are allergic to it or any of its ingredients. You should also not take famotidine if you have had reactions to other histamine H2-receptor blockers.1

Warnings for those with Kidney Disease

If you have any decreases in kidney function, you should tell your doctor before taking famotidine.1

Decreased kidney function can increase the amount of time it takes for famotidine to be cleared from your body. This can cause the drug to build up in your body and increase your risk of side effects.1

If your kidney function is severely decreased (creatinine clearance <50 mL/min), you will need to take smaller amounts of famotidine.1

Warnings for Pregnant Women

The FDA categorizes famotidine as a pregnancy Category B drug.1

This means that studies on animals have shown no negative effects on unborn babies. However, there is not enough data from human studies to prove drug is completely safe.14

Your doctor will decide if the benefits outweigh the risks in your case.1

Warnings for Nursing Women

Famotidine can get into human breast milk.1

Studies on animals suggest that famotidine in breastmilk can decrease the growth rate in the baby.1

This has not been proven in humans, though. Since it is not clear what effect famotidine may have on an infant without acid reflux, famotidine therapy is discouraged for nursing mothers.1

If famotidine is essential to your health, however, it may be necessary to continue taking it while nursing. Your doctor will decide if the benefits outweigh the risks in your case.1


Famotidine Compared to Similar Drugs

Famotidine vs Omeprazole (Prilosec)

Omeprazole is another drug used to decrease the amount of acid produced by the stomach.15

Omeprazole works differently than famotidine. Rather than targeting histamine receptors, omeprazole targets the acid pump in the acid-producing cells.16

This pump, called the hydrogen-potassium ATPase (H-K-ATPase), adds hydrogen ions to stomach fluid, making it acidic (Figure 1).16

Prilosec binds to H-K-ATPase and prevents it from working. This binding is permanent. Stomach acid production can only increase again when the cell makes a new H-K-ATPase.16

There is little difference between famotidine and omeprazole with regards to1,15:

  • Dosage
  • Effectiveness
  • Duration of therapy
  • Side effects

There are differences in how the body handles the drugs, however.1,15

Famotidine is removed from the body by the kidneys. Omeprazole is broken down by the liver.1,15

If you have liver disease, your doctor may choose to prescribe famotidine. If you have kidney disease, your doctor may want you to take omeprazole.1,15

Omeprazole interacts with more drugs than famotidine. Common drugs that interact with omeprazole are listed in Table 1. If you are on these or similar drugs, your doctor may choose to prescribe famotidine.1,15

Famotidine may be safer than omeprazole during pregnancy.15 Unlike famotidine, studies in animals have shown negative effects of omeprazole on unborn babies. Scientists have not confirmed these effects in humans.14

Famotidine vs Ranitidine (Zantac)

Like famotidine, ranitidine is a histamine H2-receptor inhibitor.17

Ranitidine has similar efficacy, side effects and safety. Both are category B pregnancy drugs.1,17

Effective doses of ranitidine are much larger than those of famotidine. Common dosages of ranitidine are 150-300 mg per day. Doses up to 6 g per day have been used.1,17

Ranitidine interacts with more drugs than famotidine.1,17 Common drugs that interact with ranitidine are listed in Table 1. If you take these or similar drugs, your doctor may prescribe famotidine.

Famotidine vs Cimetidine (Tagamet)

Cimetidine is a histamine H2-receptor inhibitor.18

Common dosages of cimetidine are between 400-800 mg per day. Dosage as high as 1.6 g per day have been prescribed.18

The side effects of cimetidine are similar to those of famotidine. Cimetidine is linked to an increased risk of pancreatitis, though, which is not seen with famotidine.18

Similar to famotidine, your doctor will have to adjust your dosage of cimetidine if you have kidney disease.18

Unlike famotidine, cimetidine interacts with a number of other drugs (Table 1).18

If you take these or similar drugs, your doctor may choose to prescribe famotidine.18


Table 1: Selected drugs that can interact with omeprazole, ranitidine and cimetidine.15,17,18


Ibuprofen and Famotidine (Duexis) Used Together

Famotidine is also sold in combination with ibuprofen. This mixture is sold under the brand name Duexis.2

Doctors may prescribe Duexis for you if you have a chronic inflammatory condition.2

Such conditions require long-term therapy with strong anti-inflammatory drugs, such as ibuprofen.2

Unfortunately, ibuprofen can have serious side-effects on your stomach or intestines when taken long-term.

This is because ibuprofen decreases the function of an enzyme called cyclooxygenase 1 (COX-1). COX-1 is responsible for maintaining the mucus that protects the walls of our stomach and intestines from acid.19

When ibuprofen blocks COX-1 for a long time, it can cause the protective lining of our stomachs to break down. This exposes the stomach wall to acid and can lead to ulcers.2

Duexis is supposed to help keep ulcers from forming. The hope is that lower acid levels from the famotidine will keep the stomach wall safe, even if the protective lining breaks down.2

While the risk of side effects in your stomach may be lower with Duexis, they are not eliminated.2

And Duexis presents the same risks as ibuprofen alone for other organ systems, such as an increased risk of2:

  • Heart attack
  • Stroke
  • New or worsening asthma
  • New or worsening high blood pressure
  • Kidney damage
  • Liver damage

If you have a history of any of these conditions, it is unsafe to take Duexis.2

It is also unsafe for you to take Duexis during the third trimester of a pregnancy. It can cause the blood vessel that routes the baby’s blood away from the lungs to close.2

If this blood vessel closes, the baby will begin breathing in the womb. This is extremely dangerous for the baby and can result in death.2


Famotidine Drug Interactions

Studies have found no major interactions between famotidine and any other prescription drugs.1

Famotidine and Alcohol

Studies suggest that histamine H2-receptor inhibitors can increase the amount of alcohol you absorb from drinks.20,21

H2-receptor inhibitors block the activity of the alcohol dehydrogenase enzyme. This enzyme normally breaks down alcohol in the stomach before it can be absorbed. Blocking this enzyme may increase the amount of alcohol that gets into your blood.21

Compared to the other H2-receptor inhibitors, famotidine inhibits alcohol dehydrogenase the least.21

Doctors believe that any increases in blood alcohol levels from famotidine will be small.20 They do not believe it is necessary to avoid alcohol while taking famotidine.1,20,21


Abuses of Famotidine

Though famotidine can have side effects that affect the brain, it is not addictive. The FDA has not classified famotidine as a controlled substance.1,22

The risk for abuse of famotidine is very low.


Famotidine FAQs

  • How often can you take famotidine?

You should take famotidine as often as your doctor asked you to.1

To treat an ulcer or acid reflux, this may be once or twice per day.1

If you are taking famotidine for MEN-1 or Zollinger-Ellison Syndrome, your doctor may want you to take famotidine every 6 hours.1

  • How much famotidine can I take in a day?

You should take the amount of famotidine prescribed by your doctor.

Your doctor has prescribed the lowest dose that can control your symptoms. This is to minimize your risk of developing side effects.1

If you feel that famotidine is not managing your symptoms, you should speak to your doctor.

  • Which is better – famotidine or omeprazole?

The answer to this question depends on your medical history.

Both drugs work about equally well to decrease stomach acid production.

They have similar side effects. And you have to take them for about equal amounts of time.1,15

However, if you have certain medical conditions or take certain drugs, one may be safer for you than the other. Your doctor will determine if famotidine or omeprazole is better for you.1,15

  • Is Duexis a narcotic?

No. Duexis is a combination of famotidine and ibuprofen. Famotidine is a histamine H2-receptor inhibitor. Ibuprofen is a non-steroidal anti-inflammatory drug. Neither are a narcotic.2


  1. Merck & Co, Inc. Pepcid (Famotidine) Tablettes. Last updated 2006. Accessed August 10, 2017. PDF.
  2. Horizon Pharma USA, Inc. Duexis Prescribing Information. Last updated June, 2017. Accessed August 10, 2017. PDF.
  3. US Department of Health and Human Services. FDA. FDA Approved Drug Products: Fluxid. Last updated N/A. event=overview.process&ApplNo=021712. Acessed August 11, 2017.
  4. Schubert ML, Peura DA. Control of gastric acid secretion in health and disease. Gastroenterology. 2008;134(7):1842-1860.
  5. McColl KE. Pathophysiology of duodenal ulcer disease. European journal of gastroenterology & hepatology. 2012;9 Suppl 1:S9-12; discussion S12.
  6. Prabhu V, Shivani A. An overview of history, pathogenesis and treatment of perforated peptic ulcer disease with evaluation of prognostic scoring in adults. Annals of medical and health sciences research. 2014;4(1):22-29.
  7. Boeckxstaens GE, Smout A. Systematic review: role of acid, weakly acidic and weakly alkaline reflux in gastro-oesophageal reflux disease. Alimentary pharmacology & therapeutics. 2010;32(3):334-343.
  8. Epelboym I, Mazeh H. Zollinger-Ellison syndrome: classical considerations and current controversies. The oncologist. 2014;19(1):44-50.
  9. Nurmatov UB, Rhatigan E, Simons FE, Sheikh A. H2-antihistamines for the treatment of anaphylaxis with and without shock: a systematic review. Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology. 2014;112(2):126-131.
  10. Tleyjeh IM, Abdulhak AB, Riaz M, et al. The association between histamine 2 receptor antagonist use and Clostridium difficile infection: a systematic review and meta-analysis. PloS one. 2013;8(3):e56498.
  11. Cohen SH, Gerding DN, Johnson S, et al. Clinical practice guidelines for Clostridium difficile infection in adults: 2010 update by the society for healthcare epidemiology of America (SHEA) and the infectious diseases society of America (IDSA). Infection control and hospital epidemiology. 2010;31(5):431-455.
  12. Corley DA, Kubo A, Zhao W, Quesenberry C. Proton pump inhibitors and histamine-2 receptor antagonists are associated with hip fractures among at-risk patients. Gastroenterology. 2010;139(1):93-101.
  13. Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. Jama. 2013;310(22):2435-2442.
  14. Services UDoHaH. FDA Pregnancy Categories.
  15. AstraZeneca Pharmaceuticals LP. Prilosec Prescribing Information. Last updated September 2012. 019810s096lbl.pdf. Accessed August 11, 2017. PDF.
  16. Sheen E, Triadafilopoulos G. Adverse effects of long-term proton pump inhibitor therapy. Digestive diseases and sciences. 2011;56(4):931-950.
  17. GlaxoSmithKline. Zantac Prescribing Information. Last updated 2004.,019675s031,020251s016lbl.pdf. Accessed August 11, 2017. PDF.
  18. GlaxoSmithKline. Tagamet Product Information. Last updated 2009. Accessed August 11, 2017. PDF.
  19. Vane JR, Botting RM. Mechanism of action of anti-inflammatory drugs. Scandinavian journal of rheumatology Supplement. 1996;102:9-21.
  20. Burnham DB, Miller D, Karlstadt R, Friedman CJ, Palmer RH. Famotidine increases plasma alcohol concentration in healthy subjects. Alimentary pharmacology & therapeutics. 1994;8(1):55-61.
  21. Caballeria J, Baraona E, Deulofeu R, Hernandez-Munoz R, Rodes J, Lieber CS. Effects of H2-receptor antagonists on gastric alcohol dehydrogenase activity. Digestive diseases and sciences. 1991;36(12):1673-1679.
  22. Drug Enforcement Agency. Controlled Substances. Last updated July 7, 2017. Accessed August 14, 2017. PDF.


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