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Pharmacology · Drugs and Prescriptions

Tamoxifen

Tamoxifenum

Tamoxifen is an antineoplastic agent belonging to the group of selective estrogen receptor modulators (SERMs). The drug is used in the treatment of hormone-dependent tumors by blocking the action of estrogens in breast tissue.

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Pharmacological groupAntineoplastic agent, selective estrogen receptor modulator (SERM).
Dosage formTablets 0.01 g; 0.02 g; 0.03 g and 0.04 g.
Mechanism of actionCompetitive blockade of estrogen receptors, inhibition of hormone-dependent cell growth.
Route of administrationOral, daily dose 0.02–0.04 g.
How to write a prescription
Rp.: Tab. Tamoxifeni 0,02
D.t.d. N 30
S. Внутрь по 1 таблетке (0,02 г) 1 раз в сутки независимо от приёма пищи

Alternative prescriptions: Tabulettas Tamoxifeni 0.02; Tab. Tamoxifeni citratis 0.02; Tab. Tamoxifeni 0.01

Dosage form
Tabs. 0.01; 0.02; 0.03 and 0.04 g
Administration
Oral 0.02-0.04 g
Group
Antineoplastic agents
2 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Mechanism of action

Tamoxifen is a triphenylethylene derivative. Its action is based on competition with estradiol for binding to $\alpha$- and $\beta$-estrogen receptors. Upon binding to the receptor, the drug induces specific conformational changes that determine its tissue specificity. Depending on the tissue type and the set of coactivators or corepressors, tamoxifen can exhibit both antagonist and agonist properties.

Pharmacological effects

The effects of the drug depend on the receptor localization:

  • Breast tissue: acts as an antagonist, blocking cell proliferation.
  • Bone tissue: exhibits agonist properties, helping to prevent osteoporosis.
  • Endometrium: acts as a partial agonist, creating a risk of hyperplasia with prolonged use.
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Indications for use

The primary indication is breast cancer in postmenopausal women. The drug inhibits the hormone-dependent growth of tumor cells, and this effect is independent of the cell cycle phase.

Side effects and risks

Tamoxifen administration is associated with several adverse reactions:

  • Hypoestrogenic manifestations: hot flashes, sweating, palpitations.
  • Specific risks: endometrial hyperplasia and cancer (due to the agonistic effect on the uterus), thromboembolism.
  • Other: visual disturbances, skin rash, dizziness, gastrointestinal disorders.
  • Important: the development of hypercalcemia is an absolute indication for immediate discontinuation of the drug.

Prescription details

Tamoxifen is a substrate of the CYP1A2 isoenzyme, which requires consideration of drug interactions. The drug is not a pure estrogen, and its efficacy in postmenopause is due to the depletion of the estrogen receptor pool (down-regulation) in target tissues.

How to memorize

Tamoxifen: T-T-T (Tissue-specific, Triphenylethylene, Treatment of breast cancer). Remember: breast — blockade, bones — support, uterus — risk.

Class and exam questions

Why does tamoxifen increase the risk of endometrial cancer?

In endometrial tissue, tamoxifen exhibits properties of a partial estrogen receptor agonist, which stimulates proliferative processes in the uterus with prolonged administration.

What is the advantage of raloxifene over tamoxifen?

Raloxifene is an antagonist in both the breast and the endometrium, so it does not increase the risk of hyperplasia and uterine cancer.

What happens to estrogen receptors upon exposure to tamoxifen?

An unproductive "receptor-drug" complex is formed, followed by depletion of the receptor pool (down-regulation).

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What else to study on this topic

  • Comparison of the safety profiles of tamoxifen and toremifene.
  • The role of coactivators and corepressors in the tissue specificity of SERMs.
  • Interaction of tamoxifen with the cytochrome P450 system (CYP1A2).
  • Differences in the mechanisms of action of tamoxifen and fulvestrant (a pure antagonist).
  • Management tactics for patients who develop hypercalcemia during therapy.

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