key facts

Legal Status (US): Not listed as a controlled substance

Average Dose:
Aromatase inhibition: 100-200mg/day (tra nsdermal). 150-250mg/day (oral)
Anabolic effects : 800-1000mg/day (oral)

Average Cycle Length: 2-4 weeks

Formestane is a steroidal aromatase inhibitor, known as a suicidal inhibitor because it permanently binds to the aromatase enzyme.

Formestane was originally used as an injectable for breast cancer patients, but due to its possible androgenic effects it has largely been replaced by non-steroidial AIs in the medical community. Most of its use is now is limited to the bodybuilding community since it is available as a legal dietary supplement for reducing estrogen and increasing testosterone production.

Although formestane can effectively reduce estrogen through oral consumption, its low oral bioavailability has lead to the development of several transdermal based products (which appear to offer higher efficacy at a lower dose).

Relative to 6-oxo and ATD, Formestane is a more potent aromatase inhibitor, which appears to effectively reduce natural estrogen levels by as much as 50% within several days (while higher doses may further suppress estrogen). Because of formestanes potent ability at reducing estrogen it will tend to reduce HDL levels, while increasing LDL levels, thus harming the cholesterol profile. For this reason, it is recommended to limit cycles of formestane to 8 weeks max.

Because formestane also has a strong affinity for the 5a-reductase enzyme it will reduce DHT levels in the body by effectively competing with testosterone for the 5a-reductase.
Formestane converts to the active androgen 4-hydroxytestosterone which has about half the anabolic potency, and about 25% of the androgenic potency as testosterone. This would suggest that fairly high doses of formestane (800-1000mg/day) could lead to some level of anabolic enhancement (although the amount required for this would surely lead to undesirably low estrogen levels).

Formestane is successfully used as a standalone during re-composition cycles to help reduce “bloat” and fat storage. It can also be used as an anti-estrogen to counter aromatization of aromatizing steroids.

Common Clones:
Formestane by Primordial Performance
Formex by Innovative Body Enhancement (IBE)
Formestane by Competitive Edge Labs (CEL)
Formadex by BCS LABS

the science

Chemical Name(s):
4-Hydroxyandrost-4-ene-3, 17-di one
4-Hydroxyandrostene dione

Chemical Formula: C19H26O3
Molecular Weight: 302
Q Qatio: NA
Anabolic #: NA
Androgenic #: NA
Oral Bioavailability: Estimated at 4%
AR Binding Affinity: NA
SHBG Binding Affinity: NA
Half Life: 2-3 hours oral, Transdermal: Varies by matrix

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Anabolic Pharmacology
Seth Roberts (2009)