Aromasin is the aromatase inhibitor people switch to when Arimidex has not worked for them, or when they want something that does not let estrogen bounce back. It is a breast cancer drug first, and most of what we know about it comes from those trials. That is useful, because it means there is real data on how it compares with Arimidex.
Here is what Aromasin is, how it differs from Arimidex, what it does to estrogen in men, and the side effects worth knowing.
What Aromasin is
Aromasin is the brand name for exemestane, made by Pfizer. The FDA approved it in October 1999 for breast cancer in postmenopausal women. The standard medical dose is 25 mg once a day, taken by mouth. Its half-life is about 24 hours.
It blocks aromatase, the enzyme that turns testosterone into estradiol. Less aromatase activity means less estrogen.
In Canada, exemestane is a prescription drug. In sport, all aromatase inhibitors are banned by WADA.
Why steroid users take it
When you run testosterone, or anything that converts to estrogen, some of it turns into estradiol. Too much estradiol brings water retention, puffiness, and in some men gynecomastia. An aromatase inhibitor keeps that conversion down.
Not every compound needs one. Masteron, for example, cannot convert to estrogen at all. The testosterone base in most cycles can.
Aromasin vs Arimidex
| Aromasin | Arimidex | |
|---|---|---|
| Drug | Exemestane | Anastrozole |
| Type | Steroidal | Non-steroidal |
| How it binds aromatase | Permanently. The enzyme is destroyed and has to be replaced | Temporarily. It competes for the enzyme and lets go |
| Medical dose | 25 mg a day | 1 mg a day |
| Our tablets | 25 mg, from $75 | 1 mg, 50 tablets, from $70 |
Steroidal vs non-steroidal. Exemestane is built on a steroid backbone, which is why it can act as a mild androgen at high doses. Anastrozole is not.
“Suicide” inhibition. Exemestane binds aromatase and permanently disables it. That is why people describe it as less prone to a rebound when they stop: the body has to build new enzyme. Anastrozole only blocks the enzyme while it is in your system.
What the head-to-head trial found
The largest comparison, the MA.27 trial, randomised 7,576 women with early breast cancer to exemestane 25 mg or anastrozole 1 mg a day for five years.
- Effectiveness: no significant difference in event-free or overall survival.
- Exemestane: osteoporosis was reported less often, and cholesterol looked lower.
- Exemestane: more reports of mood changes and abnormal liver function tests.
In short, they did the same job with different side effect profiles. That was in women with cancer, not in men on a cycle, but it is the best direct comparison available.
What it does to estrogen in men
In a study of young men, exemestane cut estradiol (E2) by about 35% and estrone (E1) by about 70%. It also raises LH and FSH, the signals that tell the testes to make testosterone, which is why it shows up in post-cycle plans as well as on cycle.
The risk on the other side is crashing estrogen. Men need some estradiol for joints, libido, mood, bones and cholesterol. Taking more than you need can leave you with aching joints, low sex drive and flat mood. Because exemestane’s effect is permanent at the enzyme, it is slower to undo than Arimidex if you overshoot.
The only reliable way to know where you stand is a blood test for estradiol, ideally a sensitive assay, before you start and while you run it.
Side effects
From the clinical data, the most common:
- Hot flashes and sweating
- Joint pain
- Headache
- Trouble sleeping
- Fatigue and nausea, mainly in patients with advanced cancer
- Acne and weight gain, mostly at doses above the medical one
About 20% of patients in the trials saw a drop in lymphocytes, a type of white blood cell, mostly those who already had low counts.
Where Aromasin fits
- If Arimidex works for you, there is no strong reason to switch. The trials found them equally effective.
- If you do not tolerate Arimidex, or your estradiol keeps climbing back, exemestane is the usual alternative.
- If you are worried about cholesterol, the cancer trial data leaned slightly in exemestane’s favour.
Related reading: what Arimidex is, how to reverse gyno from steroids and, for post-cycle, Nolvadex ($70) and Clomid ($70). Everything for estrogen control and recovery is on our cycle support page.
Quick answers
What is Aromasin used for?
Medically, breast cancer in postmenopausal women. Steroid users take it to keep estrogen down on cycle.
Is Aromasin better than Arimidex?
In the largest head-to-head trial they worked equally well. The differences are in side effects and in how the drug binds the enzyme.
What dose of Aromasin is used medically?
25 mg once a day, in breast cancer treatment. That is not a dose recommendation for men.
Can Aromasin crash estrogen?
Yes. Too much leaves estradiol too low, with joint pain, low libido and poor mood. Bloodwork tells you where you are.
Does Aromasin raise testosterone?
It raises LH and FSH, which can increase your own testosterone production.
For adults only. Nothing on this page is medical advice. Clinical figures from the MA.27 trial and published data on exemestane. Prices current October 2026.
