What Arimidex is

Anastrozole is a non-steroidal aromatase inhibitor. It binds the aromatase enzyme reversibly and competitively, which is the single fact that explains most of how it behaves: because the binding is reversible, enzyme activity returns as the compound clears, and suppression tracks what is present rather than accumulating. That distinguishes it from exemestane, which inactivates the enzyme permanently. Anastrozole is a triazole, the same chemical family as letrozole, and the two are frequently confused despite differing several fold in potency. It reached the market in the mid-1990s under the Arimidex name and remains the reference point against which other aromatase inhibitors in this category are described.

How Arimidex compares

Against letrozole: both are non-steroidal triazoles that work the same way, but letrozole is substantially the more potent per milligram and suppresses oestrogen more completely. Against exemestane: exemestane is a steroidal inhibitor that binds irreversibly, so its effect outlasts its presence in circulation while anastrozole's does not. Those are genuinely different pharmacological behaviours rather than brand preferences, and they are the reason all three remain in use rather than one displacing the others.