Clinical data
AHFS/Drugs.com Consumer Drug Information
  • US: C (Risk not ruled out)
Routes of
ATC code none
Pharmacokinetic data
Protein binding ~85%
Metabolism Hepatic
Excretion Renal
CAS Number 968-93-4 YesY
PubChem (CID) 13769
DrugBank DB00894 YesY
ChemSpider 13172 N
KEGG D00153 YesY
Chemical and physical data
Formula C19H24O3
Molar mass 300.39 g/mol
3D model (Jmol) Interactive image
 NYesY (what is this?)  (verify)

Testolactone (INN, USAN) (brand name Teslac) is a non-selective, irreversible, steroidal aromatase inhibitor used as an antineoplastic drug to treat advanced-stage breast cancer.[1][2][3] The drug was discontinued in 2008 and is no longer available for medical use.[3]


This drug is mainly used for treating various types of breast cancer in women who have been through menopause or whose ovaries no longer function.[4] It works by blocking the production of estrogen, which helps prevent the growth of breast cancers that are activated by estrogen. It may also prevent tumor cells from being activated by other hormones.[4] It also has been used to postpone precocious puberty because of its ability to block estrogen production.[5]

Side effects

The most common side effects include:

  • Abnormal skin sensations
  • Aches of the legs and arms
  • General body discomfort
  • Hair loss
  • Loss of appetite
  • Nausea
  • Redness of the tongue
  • Vomiting


The principal action of testolactone is reported to be inhibition of aromatase activity and the reduction in estrogen synthesis that follows. Androstenedione, a 19-carbon steroid hormone produced in the adrenal glands and the gonads, is where estrone synthesis originates and is the source of estrogen in postmenopausal women. In vitro studies report that the aromatase inhibition may be noncompetitive and irreversible, and could possibly account for the persistence of this drug's effect on estrogen synthesis after drug withdrawal.[1]

In addition to its activity as an aromatase inhibitor, testolactone also reportedly possesses some anabolic activity and weak androgenic activity via binding to and activation of the androgen receptor.[3] However, androgenic side effects such as hirsutism, acne, and voice changes have been reported in no women in clinical trials.[6]


Testolactone is a synthetic 18-oxasteroid and a D-homo-18-oxo analogue of androstenedione (androst-4-en-3,17-dione), with a six-membered lactone ring in place of the five-membered carbocyclic D-ring.[3]


  1. 1 2 Testolactone at DrugBank.ca
  2. Dunkel L (July 2006). "Use of aromatase inhibitors to increase final height". Mol. Cell. Endocrinol. 254-255: 207–16. doi:10.1016/j.mce.2006.04.031. PMID 16766117.
  3. 1 2 3 4 Thomas L. Lemke; David A. Williams (24 January 2012). Foye's Principles of Medicinal Chemistry. Lippincott Williams & Wilkins. pp. 1362–. ISBN 978-1-60913-345-0.
  4. 1 2 Testolactone facts and comparisons at Drugs.com
  5. Carel, J.-C.; Lahlou, N; Roger, M; Chaussain, JL (2004). "Precocious puberty and statural growth". Human Reproduction Update. 10 (2): 135–47. doi:10.1093/humupd/dmh012. PMID 15073143.
  6. Aurel Lupulescu (24 October 1990). Hormones and Vitamins in Cancer Treatment. CRC Press. pp. 64–. ISBN 978-0-8493-5973-6.

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