A histamine H2-receptor antagonist that inhibits stomach acid production.

Oral and intravenous administration.

Trade name Tagamet

Bioavailability is 60–70%, with a protein binding of 15–20%.

Undergoes hepatic metabolism.

Half-life of 2 hours

Excretion by the kidneys.

Primarily used in the treatment of heartburn and peptic ulcers.

Can reduce the debilitating pain and symptoms of herpes zoster, presumably by blocking the H2-receptors of T-lymphocyte suppressor cells.

May be efficacious for the treatment of chronic calcific tendinitis of the shoulder.

Cimetidine has been reported for use as an analgesic in treatments of interstitial cystitis.

Side effects can include dizziness, and headache.

A known inhibitor of many isozymes of the cytochrome P450 enzyme system and specifically CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4.

As an inhibitor of cytochrome P450 its use associated with numerous drug interactions.

By reducing the metabolism of drugs through these enzymes, cimetidine may increase their serum concentrations to toxic levels. 


Many drugs are affected, including: warfarin, theophylline, phenytoin, lidocaine, quinidine, propranolol, labetalol, metoprolol, methadone, tricyclic antidepressants, some benzodiazepines, dihydropyridine calcium channel blockers, sulfonylureas, metronidazole, and some recreational drugs such as ethanol and methylenedioxymethamphetamine (MDMA).

May decrease metabolism of hormonal contraception, and is a competitive antagonist at the dihydrotestosterone (DHT) receptor, leading to exaggerated effects of estrogens.

In women use can lead to galactorrhea.

In men use of cimetidine may rarely be associated with gynecomastia, and male sexual dysfunction.

Affects the metabolism of methadone, sometimes increasing blood levels and a higher incidence of side effects.

May interact with hydroxychloroquine.

Potentiates the effects of several opioids, including tramadol via the cytochrome P450 pathway inhibition, and can lead to overdosage.

Because of its ability to suppress the acid-mediated break down of proteins, its use can elevate the risk of developing food or drug allergies due to undigested proteins that can pass into the gastrointestinal tract where sensitization can occur.

Cimetidine can also interacts with tricyclic antidepressants and selective serotonin reuptake inhibitors, and triptans causing increased blood levels of these drugs.

A potent inhibitor of tubular creatinine secretion.

Can interfere with the metabolism of sildenafil., causing its strength and duration to increase.

Has significant anti-androgen properties at high doses that are especially noticeable in men.

It is effective for the treatment of acne and androgenic alopecia.

Not an effective agent for hirsutism or in sex hormone-associated cancers such as breast and prostate cancers..

Cimetidine’s anti-androgen properties include side effects such as galactorrhea and amenorrhea in women and gynecomastia and impotence in men.

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