- Aromatase inhibitors (AIs) lower estrogen production; they’re breast cancer drugs used off-label by men.
- Anastrozole (Arimidex) is reversible; exemestane (Aromasin) is irreversible and steroidal.
- Men need estrogen for bones, joints, libido, mood and cholesterol. Crashing it causes real harm.
- Use should be guided by estradiol bloodwork, not routine “just in case” dosing.
Aromatase inhibitors are among the most misused drugs in bodybuilding. Used carefully, they can help with estrogen-related side effects of testosterone. Used routinely, they cause problems that are often blamed on something else. This guide explains how they work, how anastrozole and exemestane differ, and how to avoid the common mistakes.
How aromatase inhibitors work
Aromatase is the enzyme that converts testosterone into estradiol. AIs block it, lowering estrogen throughout the body. In postmenopausal women with hormone-sensitive breast cancer, that slows cancer growth. In men on testosterone or aromatizing steroids, it limits the rise in estradiol.
Anastrozole vs exemestane
| Anastrozole (Arimidex) | Exemestane (Aromasin) | |
|---|---|---|
| Type | Non-steroidal, reversible | Steroidal, irreversible |
| Half-life | About 2 days | About 24 hours |
| Breast cancer dose | 1 mg daily | 25 mg daily |
| Tablets we stock | 1 mg (Genetix) | 10 mg (Zionova) |
Anastrozole’s long half-life means effects build up over days. Exemestane permanently disables the aromatase it binds, so the body must make new enzyme.
Why men need estrogen
Estradiol in men supports bone density, joint comfort, libido and erectile function, mood, and healthy cholesterol. When it’s pushed too low:
- Joint pain and cracking
- Low libido and erectile problems
- Fatigue, low mood and anxiety
- Worse HDL cholesterol
- Over time, bone loss
Low estrogen symptoms look a lot like high estrogen symptoms (low libido, mood changes). Only bloodwork tells them apart.
When AIs are used
- High estradiol on bloodwork with symptoms, such as breast tenderness or significant water retention
- Men prone to gynecomastia using aromatizing compounds
- Some doctors use them in specific cases of male infertility
For breast tissue that has already started to grow, tamoxifen is often more effective; see our Nolvadex guide. For water retention, see our water retention guide.
Bloodwork
Ask for a sensitive estradiol test (reported in pmol/L in Canada). Test before adding an AI, and again a few weeks after any change. Book through your family doctor or LifeLabs or Dynacare.
Legal status in Canada
Anastrozole and exemestane are prescription drugs in Canada (on Health Canada’s Prescription Drug List). They aren’t controlled substances.
Buying in Canada
We stock Arimidex Genetix Pharma (1 mg anastrozole, 50 tablets) and Zionova Aromasin (10 mg exemestane, 50 tablets). See the PCT page for live prices.
Frequently asked questions
Do I need an AI on testosterone?
Many men don’t. Use should be based on high estradiol with symptoms, confirmed by bloodwork.
What are symptoms of low estrogen in men?
Joint pain, low libido, erectile problems, fatigue, low mood and worse cholesterol.
Arimidex or Aromasin?
Both lower estrogen. Anastrozole is reversible with a long half-life; exemestane is irreversible and steroidal.
Are aromatase inhibitors legal in Canada?
They’re prescription drugs and not controlled substances.
Products mentioned in this guide
This article is general information for adults in Canada, not medical advice. Talk to a doctor or pharmacist before using any prescription drug, anabolic steroid or research compound, and get bloodwork done. If you’re in crisis, call or text 9-8-8 (Suicide Crisis Helpline) any time.
