Exemestane
Steroidal, irreversible ('suicidal') aromatase inhibitor developed for post-menopausal breast cancer. In the PED context it is used to blunt oestrogen conversion from aromatising androgens. Because it is androgenic and does not raise SHBG the way non-steroidal AIs can, it is often favoured, but the recurring error is aggressive dosing that crashes oestradiol and produces joint pain, low libido and adverse lipids.
01 Overview
Exemestane binds the aromatase enzyme covalently and permanently inactivates it, so enzyme activity only returns as new aromatase is synthesised. A single 25 mg dose suppresses whole-body aromatisation by roughly 97-98% in post-menopausal women. Unlike letrozole and anastrozole it is a steroid structurally related to androstenedione, which gives it mild intrinsic androgenic activity and a relatively neutral-to-favourable effect on lipids at label doses.
Among men managing aromatising cycles it is used to keep oestradiol in a functional range rather than to eliminate it. The common mistake is treating any oestrogenic symptom as a reason to escalate the dose; oestradiol is required for libido, joint comfort, bone density and healthy lipids, and over-suppression produces its own distinct and often worse symptom cluster.
02 Mechanism
Irreversible steroidal inactivator of the aromatase (CYP19A1) enzyme, blocking conversion of androgens to oestrogens. Enzyme function only recovers as new aromatase protein is synthesised.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Oestrogen control (low) | 6.25–12.5 mg/day | Oral | Off-label PED use; often dosed every other day. Titrate to bloodwork, not to feel. |
| Oestrogen control | 12.5–25 mg/day | Oral | Upper end risks over-suppression on all but the most aromatising cycles. |
| Breast cancer (label) | 25 mg/day | Oral | FDA-approved dose for advanced/early breast cancer in post-menopausal women. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Reduced oestradiolMarked, dose-dependent fall in circulating oestradiol; controls gynaecomastia and oestrogenic water retention. | -85 to -98% | Clinical | |
| Neutral-to-favourable lipid profileAt label dose exemestane is comparatively lipid-neutral, partly attributed to its weak androgenic metabolite. | vs non-steroidal AIs | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Oestradiol over-suppressionCrashed oestradiol causes low libido, erectile difficulty, low mood, fatigue and dry, painful joints. | Moderate | Common with over-dosing | Clinical | |
| Arthralgia / joint stiffnessAching, stiff joints, a well-documented class effect of aromatase inhibition. | Moderate | Common | Clinical | |
| Reduced bone mineral densitySustained oestrogen suppression accelerates bone loss over months to years. | Moderate | Common with prolonged use | Clinical |
06 Commonly used with
What exemestane is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Support & ancillaries | ||
| Testosteronearomatising base | Run with testosterone as a suicidal AI to permanently knock out aromatase and control estrogenic sides.Trade-off: Irreversible enzyme inhibition means an overshoot lingers, crashing estrogen with lipid, joint and libido fallout. | |
| Dianaboloral kickstart | Chosen during heavy oral aromatisers because it slightly raises free testosterone and IGF-1 while cutting estrogen.Trade-off: It does nothing for the liver and BP burden of Dianabol and can push lipids further the wrong way. | |
| hCGon-cycle | Added to counter the extra estrogen produced when hCG drives testicular steroidogenesis.Trade-off: Combining both makes estradiol swing unpredictably and easy to over-suppress. | |
| Post-cycle | ||
| TamoxifenPCT | Occasionally bridged into PCT to keep estrogen down while the SERM restarts the axis.Trade-off: Low estrogen during recovery can slow the very LH/FSH rebound PCT is meant to achieve. | |