Antiestrogens, also known as estrogen antagonists or estrogen blockers, are a class of drugs which prevent estrogens like estradiol from mediating their biological effects in the body. They act by blocking the estrogen receptor (ER) and/or inhibiting or suppressing estrogen production.[1][2] Antiestrogens are one of three types of sex hormone antagonists, the others being antiandrogens and antiprogestogens.[3]

Drug class
Fulvestrant, a steroidal antiestrogen and a drug used in the treatment of breast cancer.
Class identifiers
SynonymsEstrogen antagonists; Estrogen blockers; Estradiol antagonists
UseBreast cancer; Infertility; Male hypogonadism; Gynecomastia; transgender men
ATC codeL02BA
Biological targetEstrogen receptor
Chemical classSteroidal; Nonsteroidal (triphenylethylene, others)
External links
In Wikidata

Types and examples

Antiestrogens include selective estrogen receptor modulators (SERMs) like tamoxifen, clomifene, and raloxifene, the ER silent antagonist and selective estrogen receptor degrader (SERD) fulvestrant,[4][5] aromatase inhibitors (AIs) like anastrozole, and antigonadotropins including androgens/anabolic steroids, progestogens, and GnRH analogues.

Although aromatase inhibitors and antigonadotropins can be considered antiestrogens by some definitions, they are often treated as distinct classes.[6] Aromatase inhibitors and antigonadotropins reduce the production of estrogen, while the term "antiestrogen" is often reserved for agents reducing the response to estrogen.[7]

Medical uses

Antiestrogens are used for:

Side effects

Side effects of antiestrogens include hot flashes, osteoporosis, breast atrophy, vaginal dryness, and vaginal atrophy. In addition, they may cause depression and reduced libido.


Ethamoxytriphetol (MER-25) was the first antagonist of the ER to be discovered,[8] followed by clomifene and tamoxifen.[9][10]


  1. "Definition of antiestrogen - NCI Dictionary of Cancer Terms, Definition of antiestrogen - NCI Dictionary of Cancer Terms".,
  2. "antiestrogen" at Dorland's Medical Dictionary
  3. Judi Lindsley Nath (2006). Using Medical Terminology: A Practical Approach. Lippincott Williams & Wilkins. pp. 977–. ISBN 978-0-7817-4868-1.
  4. Eckhard Ottow; Hilmar Weinmann (8 September 2008). Nuclear Receptors as Drug Targets. John Wiley & Sons. pp. 164–165. ISBN 978-3-527-62330-3.
  5. Bruce A. Chabner; Dan L. Longo (8 November 2010). Cancer Chemotherapy and Biotherapy: Principles and Practice. Lippincott Williams & Wilkins. pp. 660–. ISBN 978-1-60547-431-1.
  6. Riggins RB, Bouton AH, Liu MC, Clarke R (2005). "Antiestrogens, aromatase inhibitors, and apoptosis in breast cancer". Vitam. Horm. Vitamins & Hormones. 71: 201–37. doi:10.1016/S0083-6729(05)71007-4. ISBN 9780127098715. PMID 16112269.
  7. Thiantanawat, Apinya; Long, Brian; Brodie, Angela (2003-11-15). "Signaling Pathways of Apoptosis Activated by Aromatase Inhibitors and Antiestrogens". The Journal of Cancer Research. Retrieved 2015-04-13.
  8. Philipp Y. Maximov; Russell E. McDaniel; V. Craig Jordan (23 July 2013). Tamoxifen: Pioneering Medicine in Breast Cancer. Springer Science & Business Media. pp. 7–. ISBN 978-3-0348-0664-0.
  9. V Craig Jordan (27 May 2013). Estrogen Action, Selective Estrogen Receptor Modulators and Women's Health: Progress and Promise. World Scientific. pp. 7, 112. ISBN 978-1-84816-959-3.
  10. Walter Sneader (23 June 2005). Drug Discovery: A History. John Wiley & Sons. pp. 198–199. ISBN 978-0-471-89979-2.

 This article incorporates public domain material from the U.S. National Cancer Institute document "Dictionary of Cancer Terms".

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