Anastrozole Reference

Plain English

What it is

Anastrozole, sold under the brand name Arimidex, is an FDA-approved prescription pill known as a non-steroidal aromatase inhibitor. It blocks the enzyme the body uses to make estrogen, so it lowers estrogen levels.

What people use it for

Its approved use is treating a common type of breast cancer (hormone-receptor-positive) in women who have gone through menopause. It has also been studied in older men with low testosterone, and some men on testosterone therapy use it off-label, under a prescriber, to bring down estrogen.

What the science shows

The breast-cancer evidence is strong and comes from large, well-run trials. In a study of older men with low testosterone, it raised testosterone and lowered estrogen but also lowered bone density in the spine, and the researchers concluded it did not improve bone health in these men.

The catch

It is not FDA-approved for men, and lowering estrogen too much can weaken bones; the label itself warns that bone density can drop. In sports it is banned at all times by the World Anti-Doping Agency. Any off-label use in men is a prescriber-led decision.

Reference summary

On-label breast-cancer evidence is mature and supported by large randomized trials. The off-label male-TRT use case rests on smaller studies. Burnett-Bowie 2009 JCEM (n=69 older men with low testosterone) reported that anastrozole 1 mg daily for 12 months raised testosterone and lowered estradiol but also produced an unfavorable bone-mineral-density signal (a reduction in lumbar spine BMD), which is the principal reason aromatase inhibition is not first-line in male hypogonadism management.

Regulatory and posture

Categories

Hormonal

Aliases

Arimidex, Non-steroidal aromatase inhibitor (small molecule, not a peptide)

Evidence posture

human - Off-label male use is investigational. Bone-mineral-density signal in the Burnett-Bowie trial is the historical concern.

Regulatory status

FDA-approved as Arimidex (1995) for adjuvant treatment of hormone-receptor-positive early breast cancer in postmenopausal women, first-line treatment of locally advanced or metastatic breast cancer in postmenopausal women, and treatment of advanced breast cancer in postmenopausal women with disease progression following tamoxifen. Off-label use in men on testosterone replacement therapy to control aromatization to estradiol is common clinical practice but is not an FDA-approved indication. WADA-prohibited at all times under S4 (aromatase inhibitors).

Content review status

label verified