What is an aromatase inhibitor?
An aromatase inhibitor is a medication that blocks the enzyme aromatase, preventing the conversion of testosterone to estrogen in the body during testosterone replacement therapy.
During testosterone replacement therapy, some of the injected or applied testosterone converts to estrogen through an enzyme called aromatase. Aromatase inhibitors (AIs) are drugs that prevent this conversion by blocking the aromatase enzyme. Common examples include anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin).
When estrogen levels rise unchecked during TRT, men may experience side effects like gynecomastia (breast tissue enlargement), water retention, and mood changes. By limiting estrogen production, AIs help keep hormone levels in a more balanced range. This is why some TRT providers incorporate AIs into treatment plans, typically at lower doses than those used in cancer treatment.
AIs are not always necessary for everyone on testosterone therapy. The need depends on individual response, total testosterone dose, baseline estrogen sensitivity, and other factors. Some men maintain acceptable estrogen levels without an AI, while others benefit from one. This is why dosing decisions are typically made by the prescribing clinic based on lab work and patient symptoms rather than applied uniformly.