Tibolone is a synthetic steroid hormone

Steroid hormone

A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into five groups by the receptors to which they bind: glucocorticoids, mineralocorticoids, androgens, estrogens, and progestogens...

 drug, which is fairly non-selective in its binding profile, acting as an agonist

Agonist

An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...

 at all five of the Type I steroid hormone receptor

Steroid hormone receptor

Steroid hormone receptors are found on the plasma membrane, in the cytosol and also in the nucleus of target cells. They are generally intracellular receptors and initiate signal transduction for steroid hormones which lead to changes in gene expression over a time period of hours to days...

s. It is used mainly for treatment of endometriosis

Endometriosis

Endometriosis is a gynecological medical condition in which cells from the lining of the uterus appear and flourish outside the uterine cavity, most commonly on the ovaries. The uterine cavity is lined by endometrial cells, which are under the influence of female hormones...

, as well as hormone replacement therapy

Hormone replacement therapy (menopause)

Hormone replacement therapy is a system of medical treatment for surgically menopausal, perimenopausal and to a lesser extent postmenopausal women...

 in post-menopausal

Menopause

Menopause is a term used to describe the permanent cessation of the primary functions of the human ovaries: the ripening and release of ova and the release of hormones that cause both the creation of the uterine lining and the subsequent shedding of the uterine lining...

 women. Tibolone has similar or greater efficacy compared to older hormone replacement drugs, but shares a similar side effect profile. It has also been investigated as a possible treatment for female sexual dysfunction, although it is unclear whether the benefits in this application justify the known risks of the drug.

Adverse Effects

A report in September 2009 from Health and Human Services' Agency for Healthcare Research and Quality suggests that tamoxifen, raloxifene, and tibolone used to treat breast cancer significantly reduce invasive breast cancer in midlife and older women, but also increase the risk of adverse side effects.