RESEARCH MONOGRAPH · KDC-MN-276

Anastrozole

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

88/100

Third-generation aromatase inhibitor that defined the standard of care and still the cleanest tool in the class

Anastrozole is the aromatase inhibitor that quietly reshaped endocrine therapy for postmenopausal breast cancer. ICI's non-steroidal AI program in the 80s, building on the experience with aminoglutethimide (which was a mess) and the second-generation fadrozole, produced a triazole-based compound with near-complete (>97%) aromatase inhibition at clinical doses and minimal off-target activity at other steroidogenic enzymes. The ATAC trial in the early 2000s established it as superior to tamoxifen in postmenopausal hormone-receptor-positive breast cancer, which is one of the more clearcut head-to-head winners in oncology endocrine therapy.

The mechanism is textbook at this point. Reversible competitive inhibition of the CYP19 aromatase enzyme, which is the rate-limiting step in conversion of androgens (androstenedione, testosterone) to estrogens (estrone, estradiol). The high selectivity over other CYP enzymes is what gives anastrozole its clean profile relative to aminoglutethimide, which had broad steroidogenic effects.

What we like is the clinical data depth. Large adjuvant trials, prevention trials (IBIS-II), the long-tail bone-loss and cardiovascular data, the comparison to other AIs. Effect sizes are real and reproducible, the dose-response is well-mapped, and the adverse effect profile (arthralgia, bone loss, lipid effects) is well-characterized.

For research use anastrozole is the standard non-steroidal AI reference compound. If you're studying aromatase pharmacology, estrogen biosynthesis modulation, or comparing across the AI class, anastrozole is one of the two or three compounds you want as benchmarks. The in vitro IC50 values are well-established and reproducible across labs.

What we dont like is mostly clinical context rather than pharmacology. The bone loss is real and meaningful in long-term postmenopausal use, the arthralgia is dose-limiting in a subset of patients, and the lipid profile shifts are not trivial. None of these are surprises given near-complete estrogen suppression; they're predictable consequences of the mechanism.

Sourcing is excellent. Off-patent globally, multiple generic manufacturers, pharmacopoeial quality widely available, the standard form is the free base. Research-grade material is straightforward to obtain with documented HPLC purity.

Established workhorse with the underappreciated angle being how cleanly designed it is mechanistically. Reliability is high, mechanism is textbook, the long-term clinical data is exceptional. Still the reference compound.

Evidence: 95
Mechanism: 92
Reliability: 90
Safety: 78
Sourcing: 95
Value: 88
Signal: 78
Staying power: 85

Plain-language summary Intrigue 65 / 100

Anastrozole (Arimidex) is a third-generation aromatase inhibitor approved in 1995, first-line for postmenopausal hormone-receptor-positive breast cancer. It blocks the aromatase enzyme, which converts androgens (including testosterone) into estrogens. At the standard 1 mg dose, it lowers plasma estradiol by about 80 percent. In breast cancer this slows or shrinks estrogen-driven tumors. Off-label, low doses are used by anabolic steroid users to control estrogen conversion and prevent gynecomastia. Side effects include joint stiffness and accelerated bone loss (because estrogen is essential for bone in both sexes). The ATAC trial established its superiority over tamoxifen in postmenopausal women. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Non-steroidal aromatase inhibitor (third generation)

A non-steroidal aromatase inhibitor; first-line for postmenopausal ER-positive breast cancer and an off-label estrogen control agent in AAS users.

Abstract

Anastrozole (2,2'-[5-(1H-1,2,4-triazol-1-ylmethyl)-1,3-phenylene]bis(2-methylpropanenitrile); CAS 120511-73-1; molecular formula C17H19N5; molecular weight 293.37) is a non-steroidal third-generation aromatase inhibitor developed at Zeneca (now AstraZeneca) and approved by the FDA in 1995 under the trade name Arimidex. Mechanism: reversible competitive inhibition of CYP19 (aromatase), the enzyme that converts androgens (androstenedione, testosterone) to estrogens (estrone, estradiol). At a 1 mg dose in postmenopausal women, plasma estradiol is reduced by approximately 80 percent. Distinct from earlier aromatase inhibitors (aminoglutethimide) by improved selectivity and elimination of corticosteroid replacement need. Plasma half-life is approximately 50 hours; metabolism is hepatic. Approved for ER-positive postmenopausal breast cancer (adjuvant and metastatic) and for ductal carcinoma in situ. Off-label use as estrogen control in androgen-using populations is widespread (typical dose 0.25 to 0.5 mg every other day). Used as the canonical non-steroidal aromatase inhibitor in mechanism studies.

Mechanism of action

Reversible competitive aromatase (CYP19) inhibition. Reduces plasma estradiol by approximately 80 percent at clinical dose.

Reported research dose ranges

Clinical 1 mg in the published literature. Off-label estrogen control 0.25 to 0.5 mg every other day. Rodent studies 0.05 to 0.5 mg/kg.

References

Buzdar AU. Anastrozole as adjuvant therapy for early-stage breast cancer. Cancer Pract 2002.
Plourde PV, et al. Arimidex: a new oral, once-a-day aromatase inhibitor. J Steroid Biochem Mol Biol 1995.
Geisler J, et al. Influence of anastrozole, a selective, non-steroidal aromatase inhibitor, on in vivo aromatisation and plasma oestrogen levels in postmenopausal women. Br J Cancer 1996.

Read the full monograph

The full reference document is available as a research-use-only PDF download. Note: PDFs for newly added compounds may take a few hours to propagate after this article was published.

KDC-MN-276

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

Download PDF →

FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Kodiac sells research compounds for investigative use only.

Anastrozole

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

Quick actions

Categories

Help and policies

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

Adjacent monographs