Anastrozole
An aromatase inhibitor: it blocks the conversion of testosterone to estradiol, used on TRT to lower high estradiol.
FDA-approved (Arimidex) for breast cancer in women; off-label in men.
Used for
- High estradiol with symptoms on TRT
- Raising testosterone in some men (off-label)
- Breast cancer (its approved use)
How it works
Blocks aromatase, the enzyme that turns testosterone into estradiol. Men need some estradiol for bone, libido, erections, mood and fat control.
Half-life: about 2 days
What the research shows
- In older men with low testosterone, 1 mg daily for a year raised testosterone and lowered estradiol but did not improve body composition or strength.
- In the same trial, spine bone density fell on anastrozole and rose on placebo.
- When estradiol was blocked in men, fat rose and libido and erectile function fell even with testosterone held normal.
Dosing
Dosing isn’t listed on the public site. In the app, each published option is shown with its source (a drug label, a clinical guideline, a trial or community reports) and can be turned into a protocol you review.
Work out the units to draw for your vial →Side effects
- Joint aches
- Low libido, erection problems and low mood if estradiol drops too far
- Hot flashes
Cautions
- Crashing estradiol is worse than high estradiol for most men: dose by bloodwork, not by feel.
- Long-term use thins bone.
- Recheck estradiol (sensitive assay) 2–3 weeks after any change.
- Prohibited in tested sports (WADA).
Storage
Unmixed or unopened: Tablets at room temperature (20–25 °C) in a tight container.
From the Anastrozole label.
Interactions
Do not combine with tamoxifen: no added benefit in the ATAC trial, and tamoxifen lowered anastrozole levels by 27%.
Estrogen-containing products can weaken its effect.
Not a full list. Tell your doctor and pharmacist everything you take.
Reference only, not medical advice. Written for this app from the cited research. Doses marked community-reported are not from trials.