Formestane (4-hydroxyandrostenedione)
CGP-32349, Lentaron, 4-OHA, 4-OH-androstenedione
Forms: Historically a depot injection for breast cancer (Lentaron); in sport, unregulated creams and capsules.
A steroidal aromatase inhibitor that disables the enzyme permanently. Once a breast-cancer injection that paved the way for today's oral inhibitors; in sport, sold as unregulated creams.
Legal status: Not an approved medicine in most countries; sold in unregulated creams and supplements, status varies by country; prohibited in sport at all times (WADA S4.1).
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
It was the first selective aromatase inhibitor on the market, given by injection for advanced breast cancer after menopause, and was later withdrawn. In sport, steroid users apply creams or take capsules to curb estrogen from aromatizing steroids; these products are not approved medicines.
What people seek and what studies show
In postmenopausal women with breast cancer the injection lowered estradiol and worked about as well as tamoxifen. In men, and for creams or capsules, there are no studies of effects or safety: human data come from anti-doping work, such as a single skin application in six volunteers to track its breakdown. In lab tests it and several metabolites acted as androgens.
Effects
Evidence: Limited human data — some human studies, small or short
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
5 possible side effects
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
For 3 of 5 possible side effects there are specific ways to lower the chance: everyday measures, supplements and options a doctor may consider. For the rest — general advice. No measure removes a risk completely.
What is unknown cannot be lowered, only avoided; tell your doctor what you have taken.
Products obtained without a prescription are often fake, mislabeled or non-sterile, and there is no way to check at home. For legal supplements, look for third-party testing (Informed Sport, NSF).
Avoid controlling estrogen blindly; adjust only by blood tests with a doctor.
How each option helps (1)
- Regular blood tests — Testing ends guesswork use of aromatase inhibitors — prescription drugs that can push estrogen too low and harm joints, libido, mood and lipids.
Stop at the first voice change and see a doctor — early stopping matters.
How each option helps (1)
- Working with a doctor — Steroid labels say to stop at the first mild signs (hoarse voice, facial hair, clitoral growth) to prevent permanent change; checks catch them early but do not make use safe.
Gentle skin care, cleansing after training, a dermatologist if it spreads.
How each option helps (3)
- Adapalene — Reduces spots in many users. Redness, scaling, dryness and stinging are common early and usually ease; acne may look worse at first. Rarely, allergic swelling.
- Benzoyl peroxide — A first-line acne option. Dryness, redness and peeling are common at first; it bleaches hair and fabric; rarely, serious allergic reactions. Severe steroid acne needs a dermatologist.
- Zinc — Trials show a modest drop in inflamed spots, weaker than antibiotics; steroid acne is driven by androgens.
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with your doctor.
Which doctors can help
Get medical help at once if
- Deepening voice, new facial hair, clitoral enlargement — stop and see a doctor: changes can become permanent. (women)
In an emergency, call your local emergency number.
For women
Before menopause the ovaries answer an aromatase inhibitor by making more hormones, so the effect is unpredictable; its androgenic activity in lab tests is a further concern.
Myth & fact
“Formestane is natural because the body makes it, so a cream is harmless.”
Traces can form in the body, which is why anti-doping labs use isotope tests, but the products deliver a withdrawn breast-cancer drug in unknown amounts. Positive tests were confirmed at the Rio 2016 Games.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check