Anastrozole

What it is

Anastrozole blocks aromatase, the enzyme that converts androgens into oestrogen. It is a genuine and important cancer medicine. It appears in a performance context because anabolic steroids that aromatise raise oestrogen, and users take aromatase inhibitors to counter the resulting effects.

It is prescribed, in oncology, to postmenopausal women with hormone-receptor-positive breast cancer, where suppressing oestrogen is the therapeutic goal and the patient is monitored throughout treatment.

What’s claimed

• Prevention of gynaecomastia during steroid use
• Reduced water retention and a harder appearance
• Higher testosterone through feedback effects

What the evidence shows

Anastrozole unquestionably lowers oestrogen: that is well-supported and is precisely its clinical purpose (Gold). What does not follow is that lowering oestrogen in a young man is beneficial. Men need oestrogen for bone density, lipid handling, joint health, cognition and libido, and unsupervised suppression of it in this context is a recognised cause of real harm. This is the clearest case in the library of a drug whose effect is well-proven and whose use here is not.

The risks

• Skeletal: suppressed oestrogen reduces bone mineral density, and in younger men the effect of sustained suppression is poorly characterised.
• Lipids: adverse changes to cholesterol, compounding the effect of the steroids it is taken alongside.
• Sexual and mood: crushing oestrogen too far commonly produces loss of libido, erectile difficulty, joint pain and low mood.
• Prescription-only: obtained outside a prescription there is no diagnosis, no oestrogen measurement and no supervision; the three things that make its clinical use safe.

What needs monitoring

• Oestradiol and testosterone
• Lipid profile
• Bone density where suppression is sustained: all of which require a doctor.