Exemestane (Aromasin)
Steroidal "suicide" (irreversible) aromatase inhibitor. FDA-approved (1999 Pfizer). Unique: 17-hydro-exemestane metabolite is mildly androgenic – SHBG drop + visible free-Test rise. In AAS used when E2 stability or SHBG emphasis matters.
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WHAT IS EXEMESTANE (AROMASIN)?
Detailed overview
Exemestane (Aromasin) is a third-generation steroidal aromatase inhibitor developed by Pharmacia & Upjohn (now Pfizer) and FDA-approved in 1999 for postmenopausal ER+ breast cancer. Pharmacokinetically distinct from non-steroidal triazole AIs (anastrozole/letrozole): it forms an irreversible covalent bond at the active site of CYP19 aromatase – each dose permanently inactivates a portion of the aromatase pool, with recovery requiring de novo enzyme synthesis (~5-7 day half-effect-life). The exemestane parent compound has a steroidal structure (androstadiendione analog), and the 17-hydro-exemestane metabolite is a MILD androgen receptor agonist (clinically negligible anabolic effect, but SHBG-lowering, so free-Test rises measurably – documented by Lønning 2005 PMID 16091756). In AAS context two niches: (1) E2 stability where the non-rebound profile is advantageous (cycle-end taper), and (2) SHBG-emphasis stacks (free-Test boost from the 17-hydro metabolite). Aromasin is the third member of the AAS AI trifecta beside anastrozole + letrozole. WADA S4.1 – banned.
Mechanism
Steroidal "suicide" (irreversible covalent) CYP19 aromatase inhibitor – a single dose permanently inactivates a portion of the pool
Dosing (AAS)
12.5-25 mg EOD or 25 mg/day
Half-life
~27 h (parent), ~24-48 h active metabolite; pharmacodynamic effect 5-7 days
Onset
E2 reduction measurable 12-24 h, full effect 3-5 days
Legal status
FDA + EMA Rx, HU + PL approved, WADA S4.1 banned
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 8
- Joint and muscle pain (arthralgia, myalgia) and stiffness, a hallmark estrogen-deprivation effect of the AI class.
- Hot flushes, sweating and fatigue, vasomotor symptoms of rapid estrogen decline.
- Over-suppressed estradiol (crashed E2): low mood, reduced libido, dry/cracking joints, depression and erectile difficulty.
- Adverse lipid shift: lowered HDL (~10-15%) and slight LDL rise, which compounds on top of an AAS stack.
- Reduced bone mineral density (osteopenia/osteoporosis risk) and higher fracture tendency with prolonged estrogen suppression.
- Mild androgenic effects from the 17-hydro-exemestane metabolite: acne and oily skin may increase, especially stacked with aromatizing steroids.
- Headache, insomnia, dizziness and gastrointestinal complaints (nausea), common and usually mild.
- Rarely elevated liver enzymes (ALT/AST) and bilirubin; as an oral agent, dual liver monitoring is warranted alongside 17-alpha-alkylated AAS.
Contraindications · 7
- Pregnancy and breastfeeding: exemestane is teratogenic and fetotoxic (Pregnancy Category X), absolutely contraindicated.
- Premenopausal women: ineffective due to intact ovarian aromatase and may cause ovulatory/hormonal disruption and virilization, contraindicated.
- Known hypersensitivity to exemestane or any excipient of the formulation.
- Severe hepatic (Child-Pugh C) or renal impairment: disturbed metabolism and clearance with increased exposure, caution/contraindication.
- Pre-existing osteoporosis or high bone-loss risk: estrogen suppression accelerates bone loss, avoid without prior DEXA and bone protection.
- Concurrent estrogen-containing agents (HRT, phytoestrogens): they negate the aromatase inhibition, an interaction to avoid.
- Strong CYP3A4 inducers (rifampicin, carbamazepine, St. John's wort) reduce efficacy; avoid prophylactic AI use without E2 baseline bloodwork due to crashed-E2 risk.
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
Meta-analyses of phase 3 randomised controlled trials of third generation aromatase inhibitors versus tamoxifen as first-line endocrine therapy in postmenopausal women with hormone receptor-positive advanced breast cancer.
Robertson JFR, Paridaens RJ, Lichfield J, Bradbury I, Campbell C
An integrated view of aromatase and its inhibition.
Miller WR, Anderson TJ, Evans DB
Changes in bone and lipid metabolism in postmenopausal women with early breast cancer after terminating 2-year treatment with exemestane: a randomized, placebo-controlled study.
Geisler J, Lønning PE, Krag LE, Løkkevik E, Risberg T, Hagen AI, Schlichting E, Lien EA, Ofjord ES, Eide GE, Polli A, di Salle E, Paolini J
Pharmacological profiles of exemestane and formestane, steroidal aromatase inhibitors used for treatment of postmenopausal breast cancer.
Lønning PE
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The information here is for educational and scientific purposes only. Performance-enhancing compounds (AAS, prohormones, stimulants, doping agents) are illegal without prescription in Hungary and most of the EU, and carry serious health and legal risks. WADA bans them in competitive sport. This is NOT a usage guide, and we do not encourage any illegal use. If you do use them, medical supervision and regular bloodwork are ESSENTIAL. Severe endocrine, cardiovascular, hepatic and psychiatric side effects are possible.