Anastrozole is a potent, selective, non-steroidal third-generation aromatase inhibitor (AI). It works by reversibly binding to the aromatase enzyme (CYP19A1), preventing the conversion of androgens (testosterone, androstenedione) to estrogens (estradiol, estrone). For AAS users, it is the most commonly used AI for controlling estrogen-related side effects during aromatizing steroid cycles — including water retention, bloating, high blood pressure, and gynecomastia. Proper estrogen management with anastrozole allows users to run higher doses of aromatizing compounds while minimizing estrogenic sides.
Notes
Anastrozole was FDA-approved in 1995 for breast cancer treatment in postmenopausal women. Its off-label use in the bodybuilding community is widespread but often misused. The modern evidence-based approach favors using the minimum effective dose based on bloodwork rather than the old-school approach of running 1mg/day throughout a cycle. Most experienced coaches now recommend having AI on-hand but only using it if symptoms or bloodwork indicate elevated E2. The lipid impact is significant and should not be ignored — cardiovascular health is the #1 long-term risk of AAS use, and AIs worsen this.
Anastrozole competitively and reversibly binds to the aromatase enzyme (cytochrome P450 19A1). This enzyme is responsible for the final step in estrogen biosynthesis — converting testosterone to estradiol (E2) and androstenedione to estrone (E1) via aromatization. By occupying the active site of aromatase, anastrozole prevents substrate binding and halts estrogen production. At 1mg/day, it suppresses plasma estradiol by approximately 70-80% in clinical studies. Importantly, the binding is REVERSIBLE — when anastrozole is discontinued, aromatase activity returns to normal, which can cause an estrogen rebound if not managed with tapering.
Oral bioavailability is approximately 100%. Rapidly absorbed with peak plasma levels at 2 hours post-dose. Moderate protein binding (~40%). Metabolized hepatically via N-dealkylation, hydroxylation, and glucuronidation. Terminal half-life of 46-50 hours, supporting every-other-day dosing. Approximately 85% of the drug is eliminated via hepatic metabolism. No significant CYP2D6 dependency. Reaches steady state in approximately 7 days.
Typical Dose
On-cycle estrogen control: 0.25-0.5mg every other day (most common). High-dose aromatizing cycles: 0.5-1mg every other day. Sensitive individuals: 0.25mg twice weekly. Estrogen rebound management: 0.25mg EOD tapering over 2-3 weeks. Never use during PCT — it will hinder recovery.
Frequency
Every other day (EOD) is the standard dosing frequency. Some users prefer twice weekly (E3.5D). Daily dosing of 1mg is almost never needed and will crash estrogen.
Administration
Oral tablet. Can be taken with or without food. Available in 1mg tablets; most users dose fractions.
Half-Life
46-50 hours
Contraindications
Anastrozole is NOT a PCT compound and should NOT be used during post-cycle therapy. Estrogen is essential for HPTA recovery — it plays a key role in GnRH and LH signaling. Using an AI during PCT will suppress estrogen and significantly impair testosterone recovery. Discontinue anastrozole before PCT begins. If E2 is very high at PCT start, a brief 1-2 week low-dose (0.25mg EOD) taper into PCT is acceptable, but the AI must be stopped early in PCT.