Sperm Count Reduction with Testosterone Supplementation
Testosterone supplementation causes severe suppression of sperm production, with 50-70% of men achieving azoospermia (zero sperm count) at high doses, and nearly all men experiencing significant reductions in sperm count regardless of dosage. 1
Magnitude of Sperm Suppression
Dose-Dependent Effects
Testosterone enanthate at 100 mg/week suppresses sperm production in parallel with LH and FSH suppression, achieving approximately 50% reduction at the ED50 dose of 50 mg/week 1
At 300 mg/week (supraphysiological dosing), testosterone enanthate achieved sperm counts ≤0.1 million/ml in 100% of treated men by 12 weeks, though this did not reliably produce complete azoospermia in all subjects 1
The time to reach 10% of baseline sperm count averages 23-25 days with testosterone treatment, regardless of whether progestin is added 2
Mechanism of Suppression
Testosterone causes parallel dose-dependent suppression of LH, FSH, and sperm production through negative feedback on the hypothalamic-pituitary-gonadal axis 1
Testicular testosterone levels decline to approximately 2% of control levels during exogenous testosterone administration, despite maintained dihydrotestosterone levels 2
The primary mechanisms include marked inhibition of spermatogonial maturation (Apale→B transition) and striking inhibition of spermiation (sperm release from seminiferous tubules) 2
Clinical Implications
Fertility Considerations
Men receiving testosterone supplementation should be counseled that sperm production will be severely suppressed or eliminated, making conception difficult or impossible during treatment 1, 2
Recovery of spermatogenesis after testosterone discontinuation is expected but not immediate, as the suppression affects multiple stages of germ cell development 2
Important Caveats
Even at clearly supraphysiological doses (300 mg/week), testosterone does not reliably induce complete azoospermia in all normal men, with 50-70% achieving zero sperm count 1
The addition of progestins (like medroxyprogesterone acetate) hastens the onset of FSH/LH suppression but does not significantly change the ultimate degree or speed of sperm count suppression 2
Germ cell suppression occurs rapidly, with type B spermatogonia and early spermatocytes showing significant reductions within 2 weeks of combined testosterone-progestin treatment 2
Monitoring Recommendations
Serum inhibin B decreases to approximately 55% of baseline by 12 weeks with testosterone plus progestin, serving as a marker of spermatogenic suppression 2
Men desiring future fertility should avoid testosterone supplementation entirely, as the degree of suppression is profound and affects the fundamental process of sperm production 1, 2