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Also indexed as: Tagamet, Tagamet HB


Cimetidine is a member of the H-2 blocker (histamine blocker) family of drugs that prevents the release of acid into the stomach. Cimetidine is used to treat stomach and duodenal ulcers, reflux of stomach acid into the esophagus, and Zollinger-Ellison syndrome. Cimetidine is available as a prescription drug and as a nonprescription over-the-counter product for relief of heartburn.

Summary of Interactions with Vitamins, Herbs, and Foods
In some cases, an herb or supplement may appear in more than one category, which may seem contradictory. For clarification, read the full article for details about the summarized interactions.

Beneficial May Be Beneficial: Depletion or interference—The medication may deplete or interfere with the absorption or function of the nutrient. Taking these nutrients may help replenish them.


Vitamin B12

Vitamin D

Avoid Avoid: Reduced drug absorption/bioavailability—Avoid these supplements when taking this medication since the supplement may decrease the absorption and/or activity of the medication in the body.


Avoid Avoid: Adverse interaction—Avoid these supplements when taking this medication because taking them together may cause undesirable or dangerous results.


Side effect reduction/prevention

None known

Supportive interaction

None known

An asterisk (*) next to an item in the summary indicates that the interaction is supported only by weak, fragmentary, and/or contradictory scientific evidence.

Interactions with Dietary Supplements

Stomach acid may facilitate iron absorption. H-2 blocker drugs reduce stomach acid and are associated with decreased dietary iron absorption.1 People with ulcers may also be iron deficient due to blood loss and benefit from iron supplementation. Iron levels in the blood can be checked with lab tests.

In healthy volunteers, a magnesium hydroxide/aluminum hydroxide antacid, taken with cimetidine, decreased cimetidine absorption by 20 to 25%.2 People can avoid this interaction by taking cimetidine two hours before or after any aluminum/magnesium-containing antacids, including magnesium hydroxide found in some vitamin/mineral supplements. However, the available studies do not clearly indicate if magnesium hydroxide was the problem and may not need to be avoided.

Vitamin B12
Hydrochloric acid is needed to release vitamin B12 from food so it can be absorbed by the body. Cimetidine, which reduces stomach acid, may decrease the amount of vitamin B12 available for the body to absorb.3 The vitamin B12 found in supplements is available to the body without the need for stomach acid. Lab tests can determine vitamin B12 levels in people.

Vitamin D
Cimetidine may reduce vitamin D activation by the liver.4 Lab tests can measure activated vitamin D levels in the blood. Forms of vitamin D that do not require liver activation are available, but only by prescription.

Interactions with Foods and Other Compounds

Cimetidine may be taken with or without food.

Caffeine is found in coffee, tea, soft drinks, chocolate, guaraná (Paullinia cupana), nonprescription over-the-counter drug products, and supplement products containing caffeine or guaraná. Cimetidine may decrease the clearance of caffeine from the body, causing increased caffeine blood levels and unwanted actions.5 People taking cimetidine may choose to limit their caffeine intake to avoid problems. They should read food, beverage, drug, and supplement labels carefully for caffeine content.


1. Aymard JP, Aymard B, Netter P, et al. Haematological adverse effects of histamine H2-receptor antagonists.Med Toxicol Adverse Drug Exp 1988;3:430–48.

2. Bachmann KA, Sullivan TJ, Jauregui L, et al. Drug interactions of H2-receptor antagonists. Scand J Gastroenterol Suppl 1994;206:14–9.

3. Salom IL, Silvis SE, Doscherholmen A. Effect of cimetidine on the absorption of vitamin B12. Scand J Gastroenterol 1982;17:129–31.

4. Anonymous. Cimetidine inhibits the hepatic hydroxylation of vitamin D. Nutr Rev 1985;43:184–5 [review].

5. Threlkeld DS, ed. Central Nervous System Drugs, Analeptics, Caffeine. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and Comparisons, Feb 1998, 230–d.

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