Category · Aromatase inhibitors
Aromatase inhibitors: approved & repurposed.
Drugs that block the enzyme converting testosterone to estradiol — approved for breast cancer adjuvant therapy, with decades of large RCTs behind that use, and widely repurposed for estrogen management on testosterone protocols.
Two flavors. Anastrozole and letrozole are non-steroidal (they bind reversibly and block the active site). Exemestane is steroidal (it binds irreversibly and the enzyme has to be re-synthesized). That difference shows up clinically: exemestane crashes estrogen harder but has a gentler effect on lipids; non-steroidals are easier to titrate but tank HDL more aggressively at full doses.
Important: the FDA-approved indications (post-menopausal breast cancer adjuvant) sit at grade 10. Off-label use for estrogen management on enhanced protocols is the default in many communities but is much more sparsely studied — judge expectations accordingly.
- 10/10 · Established Anastrozole Medically: HR+ breast cancer in postmenopausal women (adjuvant, metastatic, and risk-reduction). Off-label/non-medical: used by men alongside steroids or TRT to suppress estrogen and raise testosterone.
- 10/10 · Established Exemestane Medically: ER-positive breast cancer in postmenopausal women (adjuvant and advanced disease), plus studied (not approved) for risk reduction. Off-label/illicit: estrogen suppression by anabolic-steroid users.
- 10/10 · Established Letrozole Medically: HR-positive breast cancer in postmenopausal women (adjuvant, extended-adjuvant, and advanced disease), plus off-label ovulation induction in infertility/PCOS. Off-label/illicit: estrogen suppression by anabolic-steroid users.
Reading this class honestly
AIs are easy to over-use. Crashed estrogen — joint pain, libido, lipid harm — is one of the most common preventable problems on cycle. The bloodwork tool flags E2 below 12 as classic over-suppression when an AI is in play. See how we grade for the 1–10 logic.