Last updated: March 2026
Anastrozole (Arimidex) is a non-steroidal aromatase inhibitor that blocks the conversion of testosterone to estradiol. Originally developed for breast cancer, it became the most prescribed AI for managing elevated estrogen on TRT. At 0.5-1mg, it suppresses estradiol by 80-90%.
Anastrozole is a competitive, reversible inhibitor of aromatase — the enzyme that converts androgens to estrogens. By blocking aromatase, it prevents testosterone from being converted to estradiol.
Anastrozole binds to the aromatase enzyme (CYP19A1), blocking its active site. This prevents the conversion of testosterone and androstenedione to estradiol and estrone. The binding is competitive and reversible — stop the drug, enzyme activity returns.
At 1mg/day, anastrozole suppresses serum estradiol by 80-90%. For TRT, much lower doses (0.25-0.5mg 2-3x/week) typically suffice. The goal is estradiol in the 20-40 pg/mL range — not crashed.
By blocking aromatization, more testosterone remains unconverted. In hypogonadal men not on TRT, anastrozole can raise testosterone by 50-100%. On TRT, this effect is less relevant since testosterone is externally supplied.
Estrogen is cardioprotective. Suppressing it with AI can worsen lipid profiles — decreased HDL, potential LDL increase. This is why minimal effective AI dosing is preferred on TRT. Monitor lipids regularly.
Data from breast cancer trials and TRT-related research.
Anastrozole dosing for TRT, PCT, and standalone testosterone optimization.
| Protocol | Dose | Frequency | Notes |
|---|---|---|---|
| TRT E2 Control | 0.25-0.5mg | 2-3x/week | Start low. Adjust based on sensitive E2 lab. Target 20-40 pg/mL. |
| TRT High Aromatizer | 0.5-1mg | 2-3x/week | Some men aromatize heavily. May need more. Labs every 6 weeks initially. |
| Standalone (No TRT) | 0.5-1mg | 2-3x/week | Raises testosterone by reducing E2 feedback. Alternative to clomiphene. |
| PCT (Controversial) | 0.25-0.5mg | EOD | Some use in PCT to control rebound E2. Others avoid — may hinder recovery. Use SERMs primarily. |
| Breast Cancer (Reference) | 1mg | Daily | FDA-approved indication. Maximum E2 suppression. Not TRT dosing. |
How anastrozole compares to other aromatase inhibitors.
Reversible. Most prescribed. May interact with tamoxifen.
Irreversible (steroidal). Better lipid profile. No tamoxifen interaction.
Most potent. 99%+ E2 suppression. Easy to crash estrogen. Fertility use.
Important interactions to consider when using anastrozole.
Controversial interaction. Some data suggests anastrozole may reduce tamoxifen's effectiveness by lowering estradiol (which tamoxifen blocks). Consider exemestane if combining AI with tamoxifen for PCT.
Primary use case. More testosterone = more substrate for aromatase. Adjust anastrozole dose based on T dose and labs. Higher T usually needs more AI.
HCG stimulates intratesticular estrogen production that anastrozole can't fully block. May need higher AI doses when using HCG. Some switch to exemestane.
If on long-term AI, consider bone-protective agents. Monitor DEXA scans. Vitamin D3/K2 supplementation recommended.
Primary research supporting anastrozole's clinical use.
Anastrozole 1mg/day superior to tamoxifen for early ER+ breast cancer. 25% reduction in recurrence. Established long-term AI safety data.
PMID: 12090977 →Anastrozole 1mg/day increased testosterone by 54% in elderly obese men. LH increased 32%. Demonstrates AI effect on HPG axis without TRT.
PMID: 14671173 →Anastrozole decreased HDL by ~10% compared to tamoxifen. LDL slightly increased. Highlights cardiovascular consideration of AI use.
PMID: 11896080 →Support supplements and monitoring supplies for AI users.
Dosing schedules, interaction warnings, and cycle protocols for 50+ compounds — all in one place.
This page is for educational purposes only. It is not medical advice. Anastrozole is a prescription medication. Use for TRT estrogen management should be under physician supervision with regular monitoring. Always consult a qualified healthcare provider.