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Cimetidine

Brand names: Tagamet HB

Cimetidine is an older H2 blocker that lowers stomach acid for heartburn. It interacts with many medicines.

Brand namesTagamet HB
Type of medicineH2 blocker (acid reducer)
Prescription?Over the counter
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

Famotidine has fewer interactions and is usually preferred.

What it's used for

  • Heartburn
  • Ulcers

How to take it

  • Take it as directed, up to 30 minutes before food that causes heartburn.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Headache
  • Dizziness
  • Breast swelling in men (long use)
Call your provider todayConfusion, especially in older adults

Warnings

  • Ask before use if you take other medicines; it affects how many are cleared.

Other medicines, foods, and alcohol

  • It raises levels of warfarin, theophylline, phenytoin, and some others.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Ask your provider.

Missed doses, overdose, and storage

If you miss a dose

This medicine is often taken only when needed. If you take it on a schedule, take a missed dose when you remember, unless it's almost time for the next one. Don't double up.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.