Cimetidine (Tagamet) was the first of a new class of ulcer drugs, called “H2 antagonists.”

It works by suppressing the secretion of stomach acid, so it is also used to treat conditions of abnormal acidity such as serious heartburn as well as helping ulcers clear up rapidly.

Although it was initially a prescription medication, once the company took it over the counter, cimetidine has been used less often for ulcers and more often for heartburn or indigestion.

Sometimes cimetidine is taken to get rid of persistent warts, although the research on this use is equivocal (The Journal of Dermatological Treatment, Feb., 2012).

Cimetidine Side Effects and Interactions

Side effects associated with cimetidine are not common. However, headache, drowsiness, dizziness and diarrhea have been reported.

Older patients may experience mental confusion or even hallucinations. Long-term use can lead to vitamin B12 deficiency, which could contribute to confusion or even masquerade as dementia in an older person.

Other adverse reactions that have been reported include impotence, breast enlargement in men, rash, hair loss, pneumonia, changes in heart rhythm, liver problems and blood alterations. Report any symptoms to your physician promptly.


Cimetidine can interact with many other drugs. The blood thinner Coumadin may become far more potent in the presence of Tagamet and can lead to dangerous bleeding. Tell your doctor right away if you experience any unusual bruising, bleeding, reddish urine or blackened stools.

Drugs That Interact Badly with Cimetidine

  • ACE inhibitors such as captopril or fosinopril
  • Anti-anxiety drugs such as chlordiazepoxide, clonazepam, clorazepate, diazepam, flurazepam or triazolam
  • Antibiotics such as cefditoren, cefpodoxime or cefuroxime,
  • Antidepressants such as amitriptyline, amoxapine, desipramine, doxepin, imipramine, nortriptyline or trimipramine
  • Antifungal medicines such as ketoconazole or terbinafine
  • Beta blockers such as acebutolol, atenolol, betaxolol, bisoprolol, carvedilol, esmolol, labetolol, metoprolol, nadolol, nebivolol, penbutolol, pindolol, propranolol or timolol
  • Calcium channel blockers such as diltiazem and verapamil
  • Cancer drugs such as dasatinib, erlotinib or pazopanib,
  • Clopidogrel
  • Drugs for HIV such as atazanavir (Reyataz) or nevirapine
  • Metformin
  • Methylphenidate
  • NSAIDs such as naproxen,
  • Quinidine
  • Sirolimus

Nonprescription drugs that interact with Tagamet include antacids, alcohol, caffeine and cigarettes. Cimetidine may interfere with absorption of iron supplements, since stomach acid enhances absorption.

Caffeine may have more impact on people taking this medicine, while cigarette smoking may tend to counteract its anti-ulcer benefits.

People taking acid-suppressing drugs such as Tagamet should not take enteric-coated peppermint oil. The enteric coating is designed to keep the oil from being absorbed until it reaches the more alkaline lower intestine. But when there is very little stomach acid, the enteric coating may dissolve prematurely, releasing the oil into the stomach.

Check with your pharmacist and physician before taking any other medication or herb in combination with Tagamet.

Special Precautions

Perhaps because Tagamet is so effective at reducing stomach acid concentrations, patients taking this medicine have higher levels of certain microorganisms in their stomachs than would normally survive there. Scientists do not yet know whether these bacteria have negative long-term consequences.

Regular supplementation with vitamins C and E might in theory provide protection against possible adverse consequences.

People with liver or kidney trouble may not be able to tolerate the usual dose of Tagamet. Ask your doctor to monitor you as you begin this medicine.

Taking the Medicine

Tagamet may be taken with food, especially if it upsets your stomach.

If antacids are needed for relief of ulcer pain, they should generally be taken at a different time.

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  1. Lucy

    I have acid reflux daily….. the usual prescription medications give me migraines. So, my doctor opted for Tagamet. I take one in the morning, and one in the evening because that’s when reflux is worst. So far no side effects, but worry about longer term usage.
    The other question I have, which my doctor cannot explain is……. why all the reflux ALL THE TIME….even with a bland diet.
    (I have 2 cups coffee in the mornings…… and that’s my only vice so I’m not giving that up).

  2. Brittni Johnson
    Minneapolis, Minnesota

    Why aren’t narcotic analgesics added to the list of medication reactions? As far as I know, these are also metabolized by the same liver enzymes as Cimetidine; or am I confusing the chemistry?

    • MattyBlack88
      Santa Barbara, CA

      You are right. Narcotic Analgesics should absolutely be on this list.

  3. Gary

    Cimetidine gets rid of hives, and mine are typically caused by stress or temperature changes.
    Wal-Mart has a bargain-priced version.

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