Overview
Aromasin is classified as a PCT (post-cycle therapy) and ancillary compound. Steroidal, irreversible (mechanism-based) aromatase inhibitor.
With a half-life of ~9 hours, Aromasin requires daily administration in most observed protocols. Taken orally, it has a bioavailability of approximately 42% via its primary route.
Half-life approximately 9 hours, but enzyme suppression persists 72+ hours as new aromatase must be synthesized. Oral bioavailability ~42%. One-compartment model.
Mechanism of Action
Aromasin's pharmacological activity involves the following key pathways:
Aromatase Inhibition
Aromasin reduces the conversion of androgens to estrogens by inhibiting the aromatase enzyme. This directly lowers circulating estrogen levels.
Irreversible Binding
Aromasin is a steroidal, irreversible (mechanism-based) aromatase inhibitor. Once bound, the enzyme is permanently inactivated and must be replaced by new enzyme synthesis.
Dosing Protocols
The following protocols represent commonly observed dosing patterns. These are observational summaries, not recommendations.
Dose
12.5 mg/day
Route
Oral
Frequency
Once daily
Duration
4-8 weeks
Dose
25 mg/day
Route
Oral
Frequency
Once daily
Duration
4-8 weeks
Frequently Asked Questions
What is exemestane and how does it work?
Exemestane (brand name Aromasin) is a third-generation steroidal aromatase inhibitor that works through irreversible “suicide inhibition.” It acts as a false substrate for the aromatase enzyme – the enzyme processes exemestane and becomes permanently inactivated in the process. The body must synthesize entirely new aromatase enzyme to restore estrogen production. This mechanism provides sustained estrogen suppression even after the drug itself is cleared.
What is the half-life of exemestane and when does it reach steady state?
Exemestane has a plasma half-life of approximately 24 hours, though its functional duration of effect extends beyond this due to its irreversible binding mechanism. The body requires 2–3 days to synthesize enough new aromatase enzyme to meaningfully restore activity. Steady-state plasma levels are reached within approximately 5 days of consistent dosing. Absorption is significantly improved when taken with a fatty meal.
What makes exemestane different from anastrozole and letrozole?
The key distinction is irreversible versus reversible inhibition. Anastrozole and letrozole reversibly bind to aromatase, meaning estrogen can rebound quickly once the drug clears. Exemestane permanently destroys the enzyme it binds to, which means there is no estrogen rebound effect upon discontinuation – estrogen returns gradually as the body builds new enzyme. Additionally, exemestane has a mildly androgenic steroidal structure and does not negatively affect SHBG levels the way some non-steroidal AIs can.
Does exemestane have androgenic effects?
Yes. Exemestane has a steroidal structure that produces mild androgenic activity. This is reflected in dose-dependent suppression of sex hormone-binding globulin (SHBG), which can increase the proportion of free testosterone available. Mild acne has been observed at higher doses as a result of this androgenic activity. These effects are generally subtle and are one reason exemestane is sometimes preferred over non-steroidal AIs in certain protocols.
What are the common side effects of exemestane?
Commonly observed effects include joint discomfort, fatigue, and headache – all related to estrogen reduction. Compared to anastrozole and letrozole, exemestane is generally observed to have a somewhat more favorable impact on bone mineral density and lipid profiles, though all AIs carry some degree of these effects. The irreversible mechanism means overcorrection takes longer to resolve, as the body must produce new aromatase enzyme rather than simply waiting for the drug to clear.
Why should exemestane be taken with food?
Exemestane absorption increases by approximately 40% when taken with a fatty meal. Without food, a significant portion of the dose is not absorbed, resulting in subtherapeutic blood levels and inconsistent estrogen management. This is one of the most commonly overlooked aspects of exemestane dosing – consistent administration with a meal containing dietary fat is considered essential for reliable effect.