Anastrozole (Arimidex)
Triazole-class non-steroidal aromatase inhibitor (AI). FDA-approved (1995 AstraZeneca) for postmenopausal ER+ breast cancer. AAS-cycle E2-control golden-standard, 0.25-1 mg EOD-2x/week titrated by bloodwork.
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WHAT IS ANASTROZOLE (ARIMIDEX)?
Detailed overview
Anastrozole (Arimidex) is a third-generation non-steroidal aromatase inhibitor (AI) of the triazole class developed by AstraZeneca (then Zeneca) and approved by the FDA in 1995 for adjuvant treatment of postmenopausal ER+ breast cancer. The ATAC trial (Buzdar 2002, PMID 12081816) demonstrated approximately 97% serum estradiol suppression at 1 mg/day through reversible competitive inhibition of the enzyme – anastrozole binds the heme group of CYP19 aromatase, blocking conversion of androgens to estrogens. In AAS context, it is the standard E2-control agent during testosterone-base cycles (Test/Tren/Mast/Dianabol): weekly dosing is bloodwork-titrated, with E2 trough target 20-30 pg/mL measured by LC-MS/MS sensitive assay (NOT ECL – ECL overestimates E2 at low levels, leading to falsely elevated readings, unnecessary anastrozole dosing, and crashed E2). Anastrozole is the AAS-PCT golden-standard among aromatase inhibitors: well documented, relatively easy to titrate, moderate lipid impact.
Mechanism
Reversible non-steroidal CYP19 aromatase inhibitor, ~97% serum E2 suppression at 1 mg/day
Dosing (AAS)
0.25-1 mg EOD-2x/week titrated by bloodwork (E2 trough 20-30 pg/mL LC-MS/MS)
Half-life
~50 hours (single daily dose, steady-state day 7)
Onset
E2 reduction measurable 24-48 h, full effect 5-7 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 · 7
- Joint and muscle pain (arthralgia, myalgia), a common AI side effect, especially wrists, knees and hands, pronounced when E2 is over-suppressed
- Excessive estrogen suppression (crashed E2): loss of libido, erectile dysfunction, lethargy, depressed mood, sleep disturbance
- Adverse lipid profile: HDL decrease (~10-20%) and LDL rise, long-term cardiovascular risk, lipid monitoring required
- Reduced bone mineral density (osteopenia, osteoporosis) and fracture risk from chronic E2 deficit, DEXA monitoring advised with long-term use
- Hot flushes and sweating, a characteristic vasomotor symptom of estrogen suppression (common in clinical trials)
- Fatigue, headache and nausea; rarely mild, transient ALT/AST elevation (<2% incidence, serious hepatotoxicity extremely rare)
- Skin rash and rarely severe skin reactions (erythema multiforme, Stevens-Johnson syndrome described on the FDA label), allergic reactions
Contraindications · 7
- Pregnancy and breastfeeding are absolute contraindications (FDA Pregnancy Category X) – risk of fetal harm and pregnancy loss, contraception mandatory in women of childbearing potential
- Premenopausal women: anastrozole is ineffective and not indicated, as ovarian aromatase activity is not adequately suppressed, causing hormonal dysfunction
- Known hypersensitivity to anastrozole or any excipient (allergic reaction)
- Severe hepatic insufficiency (Child-Pugh C): CYP3A4/CYP1A2 metabolism is impaired, clinical data lacking, avoid
- Pre-existing osteoporosis or severe bone loss: chronic E2 suppression further worsens bone density and raises fracture risk
- Concurrent tamoxifen or estrogen-containing agents: tamoxifen lowers anastrozole plasma levels and estrogens negate the treatment, combination should be avoided
- Significantly adverse cardiovascular/lipid status (ischaemic heart disease, uncontrolled dyslipidemia): the AI can further worsen the lipid profile, close monitoring or avoidance warranted
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
Influence of letrozole and anastrozole on total body aromatization and plasma estrogen levels in postmenopausal breast cancer patients evaluated in a randomized, cross-over study.
Geisler J, Haynes B, Anker G, Dowsett M, Lønning PE
An integrated view of aromatase and its inhibition.
Miller WR, Anderson TJ, Evans DB
Aromatase inhibitor mechanism: review
Brueggemeier RW, Hackett JC, Diaz-Cruz ES.
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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.