Exemestane
Exemestane is a prescription tablet that permanently blocks the aromatase enzyme and so lowers oestrogen levels. It is approved to treat oestrogen receptor-positive breast cancer in women after the menopause.
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What it is
Exemestane is a tablet medicine from the group of aromatase inhibitors, and it has a steroid structure [1]. It is sold under the brand name Aromasin and as generic versions [1]. It is used in the treatment of breast cancer in women who have been through the menopause [1]. It is a prescription-only medicine and is used under the care of a cancer specialist.
How it works
Aromatase is the enzyme that turns androgens into oestrogens. Exemestane is an irreversible, steroidal aromatase inactivator. It acts as a false substrate: the enzyme takes it up as if it were its normal target, and it then binds permanently to the enzyme's active site. This is sometimes called "suicide inhibition" [1]. The result is lower oestrogen production. Exemestane has a terminal half-life of about 24 hours, is broken down mainly by the liver enzyme CYP3A4, and is absorbed more when taken with a high-fat meal [1].
Approved medical uses
- Adjuvant treatment of oestrogen receptor-positive early breast cancer in postmenopausal women who have already had 2 to 3 years of tamoxifen, to complete a total of 5 years of hormone treatment [1].
- Advanced breast cancer in postmenopausal women whose disease has progressed after tamoxifen [1].
- It is not indicated for men or children, and safety and effectiveness in children have not been established [2].
What the research shows
- Bone health in breast cancer trials. In studies summarised in the US label, bone mineral density in the lower spine fell by about 3.1% to 3.5% at 24 months with exemestane, compared with smaller changes in the comparison groups [1].
- Side effects in early breast cancer. The most common effects reported in trials were hot flushes (21%), tiredness (16%), joint pain (15%), headache (13%), sleep problems (12%) and increased sweating (12%) [1].
- Liver tests. Rises in bilirubin were seen in 5% of women on exemestane compared with 0.8% of women on tamoxifen, and rises in alkaline phosphatase were also more common [1].
- Fertility. The prescribing information states that male and female fertility may be impaired by treatment with exemestane [2].
- Men with low testosterone or infertility. The American Urological Association (AUA) says clinicians may use aromatase inhibitors, selective oestrogen receptor modulators or hCG in men with testosterone deficiency who want to keep their fertility. This is a conditional recommendation based on lower-quality evidence, and it is an off-label use [3]. Reviewers describe these fertility approaches as not well established and note that they carry side effects [4]. Exemestane is not indicated for men [2].
Known risks and side effects
- Bone thinning: exemestane reduces bone mineral density. Bone density should be assessed at the start of treatment in people at risk of osteoporosis, and bone loss monitored during treatment [1].
- Vitamin D: vitamin D levels should be assessed before starting treatment [1].
- Not for premenopausal women [1].
- Pregnancy: animal studies showed miscarriage and harm to development. Effective contraception is needed during treatment and for 1 month after stopping [1].
- Fertility in men and women may be reduced [2].
- Common effects include hot flushes, tiredness, joint pain, headache, sleep problems, sweating and nausea [1].
- Sport: exemestane is prohibited at all times under the World Anti-Doping Agency (WADA) Prohibited List [5].
Blood tests commonly monitored
- 25-hydroxy vitamin D: the label recommends assessing this before starting treatment [1].
- Liver tests (bilirubin and alkaline phosphatase): these rose more often with exemestane than with tamoxifen in trials [1].
- Bone mineral density: not a blood test, but bone density assessment is recommended at the start and monitoring for bone loss during treatment [1].
- There are no official monitoring guidelines for exemestane in men because it is not indicated for men [2]. Reviews of aromatase inhibitors in male fertility focus on oestradiol and testosterone, the hormones these drugs act on [4].
If you and your doctor are monitoring treatment, Enhanced Training Studio keeps a private log on your phone: what you take and when, your blood test results over time, and how you feel. How tracking works.
Sources
- US Food and Drug Administration. Aromasin (exemestane) tablets prescribing information. FDA, 2024. accessdata.fda.gov
- Pfizer Medical Information. Aromasin: use in specific populations (US prescribing information). Pfizer. pfizermedical.com
- American Urological Association (Mulhall, et al.). Evaluation and Management of Testosterone Deficiency: AUA Guideline. Journal of Urology and auanet.org, 2018 (validity confirmed 2024). auanet.org
- Herati AS, Kohn TP, Kassiri B. New frontiers in fertility preservation: a hypothesis on fertility optimization in men with hypergonadotrophic hypogonadism. Translational Andrology and Urology, 2020. PMC
- World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA, 2025. Prohibited List 2026 (PDF copy hosted by CONMEBOL)
Related
Last reviewed 7 October 2026. General information, not medical advice. Found a mistake? Email [email protected].