Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
Quick facts
- Drug class
- Histamine-2 Receptor Antagonist [EPC], Histamine H2 Receptor Antagonists [MoA]
- How it is given
- oral
- Type
- human prescription drug
- RxNorm ID
- 197505
We do not publish dosing. How much of this medicine to take, how often, and for how long depends on your age, weight, kidney and liver function, other conditions and other medicines. That is a decision for the person who prescribes or dispenses it. Follow the directions on your own pack and ask your pharmacist if anything is unclear.
What it is used to treat
INDICATIONS AND USAGE Cimetidine tablets are indicated in: 1. Short-term treatment of active duodenal ulcer. Most patients heal within 4 weeks and there is rarely reason to use cimetidine tablets at full dosage for longer than 6 to 8 weeks (see DOSAGE AND ADMINISTRATION: Duodenal Ulcer ). Concomitant antacids should be given as needed for relief of pain. However, simultaneous administration of cimetidine tablets and antacids is not recommended, since antacids have been reported to interfere with the absorption of cimetidine. 2. Maintenance therapy for duodenal ulcer patients at reduced dosage after healing of active ulcer. Patients have been maintained on continued treatment with cimetidine tablets 400 mg at bedtime for periods of up to 5 years. 3. Short-term treatment of active benign gastric ulcer. There is no information concerning usefulness of treatment periods of longer than 8 weeks. 4. Erosive gastroesophageal reflux (GERD). Erosive esophagitis diagnosed by endoscopy. Treatment is indicated for 12 weeks for healing of lesions and control of symptoms. The use of cimetidine tablets beyond 12 weeks has not been established (see DOSAGE AND ADMINISTRATION: GERD ). 5. The treatment of pathological hypersecretory conditions (i.e., Zollinger-Ellison Syndrome, systemic mastocytosis, multiple endocrine adenomas).
About this medicine
DESCRIPTION Cimetidine is a histamine H 2 -receptor antagonist. Chemically it is N" -cyano- N -methyl- N' -[2-[[(5-methyl-1 H -imidazol-4-yl)methyl]thio]-ethyl]guanidine. Its structural formula is: Cimetidine contains an imidazole ring, and is chemically related to histamine. Cimetidine has a bitter taste and characteristic odor. Solubility Characteristics Cimetidine is soluble in alcohol, slightly soluble in water, very slightly soluble in chloroform and insoluble in ether. Each tablet, for oral administration, contains 200 mg, 300 mg, 400 mg or 800 mg cimetidine, USP. Inactive ingredients are: croscarmellose sodium, crospovidone, hypromellose, lecithin, magnesium stearate, microcrystalline cellulose, polydextrose, polyethylene glycol, povidone, pregelatinized starch (corn), sodium alginate, sodium lauryl sulfate, titanium dioxide, triacetin, vanillin, FD&C Blue No. 1 Aluminum Lake, FD&C Yellow No. 6 Aluminum Lake and D&C Yellow No. 10 Aluminum Lake. Structural Formula
Who should not take it
CONTRAINDICATIONS Cimetidine tablets are contraindicated for patients known to have hypersensitivity to the product.
Reported side effects
ADVERSE REACTIONS Adverse effects reported in patients taking cimetidine tablets are described as follows by body system. Incidence figures of 1 in 100 and greater are generally derived from controlled clinical studies. Gastrointestinal Diarrhea (usually mild) has been reported in approximately 1 in 100 patients. CNS Headaches, ranging from mild to severe, have been reported in 3.5% of 924 patients taking 1,600 mg/day, 2.1% of 2,225 patients taking 800 mg/day and 2.3% of 1,897 patients taking placebo. Dizziness and somnolence (usually mild) have been reported in approximately 1 in 100 patients on either 1,600 mg/day or 800 mg/day. Reversible confusional states, e.g., mental confusion, agitation, psychosis, depression, anxiety, hallucinations, disorientation, have been reported predominantly, but not exclusively, in severely ill patients. They have usually developed within 2 to 3 days of initiation of treatment with cimetidine tablets and have cleared within 3 to 4 days of discontinuation of the drug. Endocrine Gynecomastia has been reported in patients treated for 1 month or longer. In patients being treated for pathological hypersecretory states, this occurred in about 4% of cases while in all others the incidence was 0.3% to 1% in various studies. No evidence of induced endocrine dysfunction was found, and the condition remained unchanged or returned toward normal with continuing treatment with cimetidine tablets. Reversible impotence has been reported in patients with pathological hypersecretory disorders, e.g., Zollinger-Ellison Syndrome, receiving cimetidine tablets, particularly in high doses, for at least 12 months (range 12 to 79 months, mean 38 months). However, in large-scale surveillance studies at regular dosage, the incidence has not exceeded that commonly reported in the general population. Hematologic Decreased white blood cell counts in patients treated with cimetidine tablets (approximately 1 per 100,000 patients), including agranulocytosis (approximately 3 per million patients), have been reported, including a few reports of recurrence on rechallenge. […]
Interactions with other medicines
Drug Interactions Cimetidine tablets, apparently through an effect on certain microsomal enzyme systems, has been reported to reduce the hepatic metabolism of warfarin-type anticoagulants, phenytoin, propranolol, nifedipine, chlordiazepoxide, diazepam, certain tricyclic antidepressants, lidocaine, theophylline, and metronidazole, thereby delaying elimination and increasing blood levels of these drugs. Clinically significant effects have been reported with the warfarin anticoagulants; therefore, close monitoring of prothrombin time is recommended, and adjustment of the anticoagulant dose may be necessary when cimetidine tablets are administered concomitantly. Interaction with phenytoin, lidocaine, and theophylline has also been reported to produce adverse clinical effects. However, a crossover study in healthy subjects receiving either 300 mg 4 times daily or 800 mg at bedtime of cimetidine tablets concomitantly with a 300 mg twice-daily dose of theophylline extended-release tablets demonstrated less alteration in steady-state theophylline peak serum levels with the 800 mg at bedtime regimen, particularly in subjects aged 54 years and older. Data beyond 10 days are not available. (Note: All patients receiving theophylline should be monitored appropriately, regardless of concomitant drug therapy.) Dosage of the drugs mentioned above and other similarly metabolized drugs, particularly those of low therapeutic ratio or in patients with renal and/or hepatic impairment, may require adjustment when starting or stopping the concomitant administration of cimetidine tablets to maintain optimum therapeutic blood levels. Alteration of pH may affect absorption of certain drugs (e.g., ketoconazole). If these products are needed, they should be given at least 2 hours before cimetidine administration. Additional clinical experience may reveal other drugs affected by the concomitant administration of cimetidine tablets.
If too much is taken
OVERDOSAGE Studies in animals indicate that toxic doses are associated with respiratory failure and tachycardia that may be controlled by assisted respiration and the administration of a beta-blocker. Reported acute ingestions orally of up to 20 grams have been associated with transient adverse effects similar to those encountered in normal clinical experience. The usual measures to remove unabsorbed material from the gastrointestinal tract, clinical monitoring, and supportive therapy should be employed. There have been reports of severe CNS symptoms, including unresponsiveness, following ingestion of between 20 and 40 grams of cimetidine, and extremely rare reports following concomitant use of multiple CNS-active medications and ingestion of cimetidine at doses less than 20 grams. An elderly, terminally ill dehydrated patient with organic brain syndrome receiving concomitant antipsychotic agents and 4,800 mg of cimetidine intravenously over a 24-hour period experienced mental deterioration with reversal on discontinuation of cimetidine. There have been two deaths in adults who were reported to have ingested over 40 grams orally on a single occasion.
Before you take anything new
Tell your pharmacist or doctor about every medicine you take — including ones bought without a prescription, herbal products and supplements. Interactions are one of the most common avoidable causes of harm from medicines, and a pharmacist can check your full list in a couple of minutes.
This page is built from the openFDA record of the U.S. Food and Drug Administration's approved labelling for this product, effective 15 August 2019. Label text has been shortened and reformatted for readability; safety wording has not been altered in meaning. FDA labelling describes products approved in the United States — brand names, strengths, formulations and approved uses may differ in your country. Always read the leaflet that comes with your own pack. PocketsInfo is not affiliated with, and is not endorsed by, the FDA. Retrieved 2026-07-30.