Anastrozole

Ancillaries & recovery

Also known as Arimidex

A non-steroidal aromatase inhibitor, used to hold oestradiol down when an aromatising androgen pushes it up.

How it works

Reversibly binds the aromatase enzyme, blocking the conversion of testosterone to oestradiol. Because the binding is reversible, effect tracks plasma concentration and returns as the drug clears.

Oral

In the body

Half-life

2.1 days

Time to peak

2 h

90% gone after

6.9 d

Builds up to

3.53×

Steady state after about 10.5 d at once daily.

Shape of a single dose, modelled as one compartment with first-order absorption. The peak is normalised to 100% because bioavailability and volume of distribution are not published for most of these compounds.

Mean terminal elimination half-life about 50 hours in postmenopausal women, from the Arimidex label. Long enough that every other day dosing still accumulates, and long enough that an overshoot takes the better part of a week to correct.

Your notes

What happens, and when

0 min, 6 hAbsorbing, peak plasma around two hours
6 h, 3 dAromatase suppressed, oestradiol falling
3 d, 10 dClearing, oestradiol recovering

Doses

1 mgonce dailyApproved label

1 mg daily, the approved breast cancer dose. Far above what anyone managing oestradiol on an androgen protocol would use, and included only because it is the regulated figure.

125 mcg, 500 mcgtwice weekly, or every other dayCommunity practice

0.125 to 0.5 mg, titrated against symptoms and bloodwork rather than taken on a schedule. No trial supports this use; the range is what people report and nothing more.

Side effects

Joint pain and stiffness, the most common complaint and usually the first sign oestradiol is too low
Loss of libido and difficulty with erections, which is what crashed oestradiol does despite adequate testosterone
Low mood and fatigue
Falling HDL, on top of whatever the androgen is already doing to lipids
Bone mineral density loss over prolonged use
Monitor: oestradiol, ideally by a sensitive assay, since the standard one is unreliable at low male levels

Cautions

Taking a second aromatase inhibitor at the same time
Running it on a compound that does not aromatise, where there is no oestrogen to control and only harm to do
Existing osteopenia or osteoporosis
Pregnancy

Status

Prescription-only. Approved for hormone receptor positive breast cancer in postmenopausal women, not for oestrogen management in men. Banned in sport at all times as a hormone and metabolic modulator.

Sources

Reference information for personal record-keeping. Not medical advice, and not a recommendation to use any of these compounds.