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.

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 directions. Cimetidine may interact with certain prescription drugs. If you are taking a prescription asthma medicine, seizure medicine, or blood thinner, speak with a healthcare provider before using an OTC medicine containing cimetidine.

  • 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 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.
  • 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.
  • 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.
  • Talk to a healthcare provider before giving an OTC containing cimetidine to a child under the age of 12.
  • Click here for more information on giving OTCs to children.