AncillaryAromatase inhibitorAncillary
Anastrozole
Also known as Arimidex · Adex · AI
A non-steroidal aromatase inhibitor used to control oestradiol on aromatising cycles. Effective and well studied — with over-suppression, not under-dosing, the more common error.
01 Overview
Anastrozole reversibly inhibits the aromatase enzyme, lowering conversion of testosterone to oestradiol. Its clinical pedigree is in breast cancer, where the dosing is far higher than needed alongside a cycle.
The defining mistake with it is crushing oestradiol too low, which causes its own joint, libido, mood and lipid problems.
02 Mechanism
Competitive, reversible aromatase inhibitor. Lowers systemic oestradiol at source, unlike a SERM which blocks the receptor in specific tissues.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| On-cycle | 0.25–0.5 mg/wk | Oral | Titrated against a sensitive oestradiol assay — never on a fixed schedule. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Controls oestradiolCounters gynaecomastia, water retention and related blood-pressure rise | Dose-dependent | Clinical | |
| Reduces water retentionBy lowering oestrogenic fluid retention | Moderate | Observational |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Over-suppression of oestradiolThe main hazard — joint pain, low libido, poor lipids, low mood and bone loss from crushing oestradiol too far. | Moderate | Common | Clinical |
06 Legal status
United States
Prescription only
as of Jan 2026
United Kingdom
Prescription only (POM)
as of Jan 2026
07 References
Anastrozole: pharmacology and clinical useClinical review
08 Discussion0 comments
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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.