Exemestane (Aromasin)
The steroidal aromatase inhibitor every male cycle schedule borrows from female postmenopausal oncology. The entire controlled evidence base in males: one 10-day crossover study of 12 healthy young men. Everything else on the male side is extrapolation.
The short version
- 25 mg/day in healthy young men: estradiol −38%, testosterone +60%, IGF-I and lipids unaffected. That single 10-day crossover is the male database. DATA
- The label's suppression curve: effect starts at 5 mg, max 85–95% aromatase inhibition at 25 mg, whole-body aromatization −98%. DATA (postmenopausal women)
- No male data exists below 25 mg/day, or on any every-other-day / interval schedule. All micro-dosing math is untested extrapolation. DATA (an absence, verified by search)
- It is a strength problem, not a dosage problem: exemestane is the weakest of the three AIs at equal schedule. MODEL
The one male study
| Measure | 25 mg/d × 10 d | 50 mg/d × 10 d |
|---|---|---|
| Estradiol suppression (basal-trough) | −38% | −32% |
| Peak suppression (12 h post-dose) | −62 ± 14% | |
| Testosterone | +60% | +56% |
| IGF-I | unaffected | |
| Lipids | unaffected | |
The label curve — where the doses come from
Suppression starts at 5 mg, maxes at 25 mg, and outlasts the pill DATA
FDA-label pharmacology (25 mg/day in postmenopausal women): maximal suppression 85–95% of baseline aromatization, whole-body aromatization down 98%, effect beginning from 5 mg/day, maximal effect occurring 2–3 days after dose and persisting 4–5 days. Terminal half-life ~24 h — but the enzyme it destroys has to be resynthesized, which is why the effect outlasts the plasma curve.
Why “suicide inhibitor” makes interval dosing plausible — and why it stays untested MODEL
Premise (data): exemestane irreversibly inactivates aromatase; recovery requires new enzyme synthesis; suppression persists 4–5 days. Logic: a dosing interval longer than 24 h could hold comparable suppression. Prediction: an EOD or low-dose schedule would produce some stable intermediate suppression. But no male study has ever measured the result — the shape between “full label dose daily” and “nothing” is unmapped. This is titration logic, not evidence.
Steroidal means androgenic
The parent is near-inert at the AR — the metabolite is not DATA
Label pharmacology: exemestane's affinity for the androgen receptor is 0.28% of DHT's. Its main metabolite 17-hydroexemestane is ~100× more potent than parent in the same assays — and the label notes one metabolite “may contribute androgenic activity.” In a 12-subject male study this never mattered; over months of high-dose use nobody has characterized it.
Where it sits among the AIs
Head-to-head in the only comparison available: letrozole crushes estradiol harder DATA
Direct comparison in male-to-female hormonal therapy (Bertelsen 2024): estradiol 0.4 vs 0.6 pmol/L and estrone 0.2 vs 1.8 pmol/L for letrozole 2.5 mg vs exemestane 25 mg daily, P<0.001 — the one setting where two AIs were dosed against each other in humans. Exemestane is the gentler instrument.
“Letrozole > anastrozole > exemestane” potency ranking MODEL
Cross-study inference, not one trial: the ranking is assembled from separate suppression studies in separate populations with separate assays. Directionally consistent, not directly measured as a set.
Young, growing skeletons — the real caution
AI-in-boys data exists — and carries a vertebral signal DATA
Cochrane review of aromatase inhibitors in boys with short stature/delayed puberty: predicted adult height improves — but with letrozole, 45% of treated boys had vertebral-body abnormalities vs 0% of controls. Vertebral compression during rapid growth is the documented AI risk in the young skeleton. Exemestane itself has no pediatric trial at all — the only publication is a single congenital-adrenal-hyperplasia case report (one boy, 177.7 cm achieved vs 151.3 predicted).
What does not exist
No sub-25 mg male data · no interval-dosing data · no cycle-length male trial DATA
Verified by search (2026-08-31): no study of exemestane in males at any dose below 25 mg/day, none on any EOD/interval schedule in either sex, none in males beyond 10 days' duration, none in healthy adolescents. Every male dosing chart in circulation is a model built on the label curve plus one 12-man study. The 4–5-day suppression persistence makes those models reasonable. It also makes them unverified.