Cimetidine is an acid reducer active ingredient available in over-the-counter (OTC) medicines that relieve or prevent heartburn symptoms associated with acid indigestion and sour stomach. Cimetidine is part of a group of acid reducers called histamine-2 antagonists, or H2 blockers.

Symptoms Treated

Symptoms Treated

More specifically: 

Heartburn, Indigestion, Sour Stomach

Common Products

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  • Tagamet®
  • Store Brands (ex. Walmart’s “Equate” store brand or CVS Health store brand)

Dosing Information

Different types of products containing this active ingredient have different strengths. That’s why it is always important to read and follow the Drug Facts label. Most medicines warn against use of an active ingredient for longer than 7-10 days. Stop use and ask a doctor if symptoms persist.

Safety Guide

Safety Guide

Cimetidine is approved by the U.S. Food and Drug Administration (FDA) and is safe and effective when used according to the Drug Facts label.

Ask a healthcare provider before use if:

  • You are taking the asthma medicine theophylline.
  • You are taking the blood-thinning drug warfarin.
  • You are taking the seizure medicine phenytoin.
  • You have had heartburn for more than three months.
  • Your heartburn is accompanied by lightheadedness, sweating, or dizziness.
  • You have kidney disease.
  • You are experiencing chest or shoulder pain with shortness of breath; sweating; pain spreading to your arms, neck, or shoulders; or lightheadedness.
  • You have frequent chest pain, wheezing, unexplained weight loss, nausea or vomiting, or stomach pain.
  • You are pregnant or breastfeeding.
  • Talk to a healthcare provider before giving an OTC containing cimetidine to a child under the age of 12.

Do not use if:

  • You are allergic to cimetidine or other acid reducers.
  • You have trouble or pain swallowing food, you are vomiting with blood, or you have bloody or black stools.
  • You are currently using another acid reducer.

Stop use and ask a doctor if:

  • Your heartburn continues or gets worse.
  • Your stomach pain continues.
  • You need to take the medicine for more than 14 days.
  • You take too much. Immediately contact a healthcare provider or the poison control national helpline at 800.222.1222.

What are the side effects of cimetidine?

  • Headache
  • Dizziness
  • Drowsiness
  • Diarrhea
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