Reviewed on 8/25/2021

What Is Cimetidine and How Does It Work?

Cimetidine is a prescription medication used as an acid reducer. Cimetidine relieves heartburn associated with acid indigestion and sour stomach. Cimetidine also prevents heartburn associated with acid indigestion and sour stomach brought on by eating or drinking certain foods and beverages.

  • Cimetidine is available under the following different brand names: Tagamet HB.

What Are Dosages of Cimetidine?

Dosages of Cimetidine:

Adult and Pediatric Dosages:

Injectable solution

  • 150 mg/ml

Oral solution

  • 300 mg/5 ml


  • 200 mg
  • 300 mg
  • 400 mg (Rx)
  • 600 mg (Rx)
  • 800 mg (Rx)

Dosage Considerations – Should be Given as Follows:

Duodenal Ulcer (off-label)

  • Children under 16 years of age: Use only if the benefit outweighs risks
  • 20-40 mg/kg/day intravenously/orally divided every 6 hours
  • Neonates (under 28 days old): 5-20 mg/kg/day intravenously/orally divided every 8-12 hours
  • Infants: 10-20 mg/kg/day intravenously/orally divided every 6-12 hours


  • Not drug of choice in elderly because of the increased potential for confusion and drug interactions

Benign Gastric Ulcer

  • 800 mg orally each evening OR
  • 400 mg orally every 12 hours OR
  • 300 mg orally every 6 hours

Duodenal Ulcer

  • 800 mg orally each evening OR
  • 400 mg orally every 12 hours OR
  • 300 mg orally every 6 hours

Erosive Gastroesophageal Reflux Disease

  • 800 mg orally each evening OR
  • 400 mg orally every 12 hours OR


Digestive Disorders: Common Misconceptions See Slideshow

What Are Side Effects Associated with Using Cimetidine?

Common side effects of cimetidine include:

  • headache
  • dizziness
  • sleepiness
  • enlarged breasts in men
  • confusion (elderly)
  • impotence
  • diarrhea
  • nausea
  • vomiting

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Cimetidine?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

  • Severe interactions of cimetidine include:
    • astemizole
    • cisapride
    • dofetilide
    • eliglustat
    • lomitapide
    • pimozide
    • terfenadine
  • Cimetidine has serious interactions with at least 143 different drugs.
  • Cimetidine has moderate interactions with at least 193 different drugs.
  • Cimetidine has mild interactions with at least 69 different drugs.

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns, or for more information about this medicine.

What Are Warnings and Precautions for Cimetidine?


  • This medication contains cimetidine. Do not take Tagamet HB if you are allergic to cimetidine or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


  • Hypersensitivity to cimetidine or other H2 receptor antagonists

Effects of Drug Abuse

  • None

Short-Term Effects

  • See "What Are Side Effects Associated with Using Cimetidine?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Cimetidine?"


  • Antiandrogen: may cause feminization and sexual dysfunction in males

Pregnancy and Lactation

  • Cimetidine use may be acceptable during pregnancy. Either animal studies show no risk but human studies are not available or animal studies showed minor risks and human studies were done and showed no risk.
  • Cimetidine enters breast milk, therefore it is not recommended for use when breastfeeding.
Medscape. Cimetidine.

Health Solutions From Our Sponsors