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Tamoxifen chemical structure
Systematic (IUPAC) name
CAS number 10540-29-1
ATC code L02BA01
PubChem 5376
DrugBank APRD00123
Chemical data
Formula C26H29N 
Mol. weight 371.515 g/mol
563.638 g/mol (citrate salt)
Pharmacokinetic data
Metabolism Hepatic (CYP3A4, 2C9 and 2D6)
Half life 5-7 days
Excretion Fecal
Therapeutic considerations
Pregnancy cat. B3 (Au) D (US)
Legal status POM(UK) -only(US)
Routes Oral

Tamoxifen is an oral selective estrogen receptor modulator which is used in breast cancer treatment, and is currently the world's largest selling breast cancer treatment. It is used for the treatment of early and advanced breast cancer in pre- and post-menopausal women. It is also approved by the Food and Drug Administration (FDA) for the reduction of the incidence of breast cancer in women at high risk of developing the disease. It has been further approved for the reduction of contralateral (in the opposite breast) breast cancer.

Tamoxifen competes with oestrogen in the body for oestrogen receptors in breast tissue so that transcription of oestrogen-responsive genes is inhibited.

Tamoxifen was invented by ICI Pharmaceuticals (now AstraZeneca) and is sold under the brand names Nolvadex, Istubal, and Valodex. It is also available as a generic drug in a number of countries. In the United States and other countries, Tamoxifen was almost always referred to by its generic name even before its patents expired.

A rare condition occasionally treated with tamoxifen is retroperitoneal fibrosis.

Tamoxifen is sometimes used to treat gynecomastia in men. Tamoxifen is also used by bodybuilders in a steroid cycle to try and prevent or reduce drug-induced gynecomastia caused by steroids that are used in the same cycle.

Tamoxifen is also used to treat infertility in women with anovulatory disorders. A dose of 10-40 mg per day is administered in days 3-7 of a woman's cycle.

On April 17, 2006, it was announced that raloxifene is equally effective in reducing the incidence of breast cancer, but caused fewer side effects. [1] [2]


Side effects

Tamoxifen is a selective estrogen receptor modulator. Even though it is an antagonist in breast tissue it acts as partial agonist on the endometrium. Therefore endometrial changes, including cancer, are among tamoxifen's side effects. Source: Golan et al. Principles of Pharmacology page 450. For some women, tamoxifen can cause a rapid increase in triglyceride concentration in the blood. In addition there is an increased risk of thromboembolism especially during and immediately after major surgery or periods of immobility.


4-hydroxytamoxifen is a form of the drug tamoxifen that is made by the body after taking tamoxifen. It can also be made in the laboratory, and may help decrease breast density. A topical form of 4-hydroxytamoxifen is being studied in breast cancer screening.


Patients with variant forms of the gene CYP2D6 (also called simply 2D6) may not receive full benefit from tamoxifen. On Oct 18, 2006 the Subcommittee for Clinical Pharmacology recommended relabeling tamoxifen to include information about this gene in the package insert.

External links

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