FSH

Follicle-Stimulating Hormone (FSH) is a glycoprotein gonadotropin secreted by anterior pituitary gonadotrophs in response to hypothalamic GnRH pulses. It shares the α-subunit with LH and TSH but carries a distinct β-subunit that determines receptor specificity. In adult males, FSH binds the FSH receptor on testicular Sertoli cells, supporting the structural and metabolic environment required for spermatogenesis.

Reference range, adult male:

– Serum FSH: 1.5–12.4 mIU/mL
– Recovery cadence: slower than LH post-cycle — 4–8 weeks behind LH normalisation
– Inhibin B is the Sertoli-cell feedback signal that modulates FSH secretion

Suppression kinetics:

FSH suppression on exogenous androgen protocols mirrors LH suppression but at a slightly delayed time course. The mechanism includes both direct testosterone/estradiol feedback at the pituitary and indirect feedback via Sertoli-cell inhibin B production (which inhibits FSH secretion specifically, not LH). Within 14 days of cycle initiation FSH falls below detection in most users; recovery post-cycle takes longer than LH because Sertoli-cell inhibin B response lags behind testosterone restoration.

Clinical relevance — spermatogenesis monitoring:

FSH-driven Sertoli function is the rate-limiting step for spermatogenesis. Suppressed FSH halts sperm production; sperm count falls toward azoospermia within 8–12 weeks of cycle initiation in most users. de Souza & Hallak 2011, BJU International documented fertility outcomes and recovery patterns in AAS-using men. Sperm count recovery trails serum testosterone normalisation by 3–6 months in most users; longer in users with extended cycle history or 19-nor exposure.

For users planning conception during or after AAS cycles, FSH measurement is the central marker — total testosterone can normalise on PCT while FSH remains suppressed and spermatogenesis stays compromised. Semen analysis at 3 and 6 months post-PCT validates fertility recovery; FSH and inhibin B measurements support the interpretation.

The hCG vs HMG distinction:

hCG mimics LH and stimulates Leydig-cell testosterone production but does not address Sertoli-cell function. For users requiring both testosterone restoration and spermatogenesis recovery, the clinical literature supports combined hCG + recombinant FSH (or human menopausal gonadotropin, HMG, which contains both LH and FSH activity). Hsieh et al. 2013, J Sexual Medicine documented the combined-protocol approach for fertility-prioritising recovery.

Persistent FSH elevation with low testosterone:

An elevated FSH (>12 mIU/mL) combined with low testosterone post-cycle is the primary testicular failure pattern. The pituitary is signalling appropriately but the testes are not responding. Causes include extended cycle-induced Leydig and Sertoli desensitisation, unmasked pre-existing testicular insufficiency (Klinefelter syndrome, prior orchitis, undescended testicle history), or rare cases of true gonadal damage from aggressive multi-year cycling. Endocrinology referral is the appropriate response; structured intervention with hCG, recombinant FSH, or LH analogue may restore function partially.

Bloodwork integration:

FSH should be measured alongside LH, total and free testosterone, sensitive estradiol, SHBG, and (where fertility matters) inhibin B and semen analysis. The integrated picture distinguishes central from peripheral failure and informs the recovery intervention sequence.