The effect of 5alpha-reductase inhibition with dutasteride and finasteride on semen parameters and serum hormones in healthy men.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 17299062 · doi:10.1210/jc.2006-2203
What was done
In a double-blind, placebo-controlled randomized trial, 99 healthy men were assigned to receive dutasteride 0.5 mg daily (n = 33), finasteride 5 mg daily (n = 34), or placebo (n = 32) for 52 weeks, followed by a 24-week untreated follow-up period. Blood and semen samples collected at baseline, 26 weeks, 52 weeks, and 24 weeks post-treatment were evaluated for testosterone, dihydrotestosterone (DHT), total sperm count, sperm concentration, semen volume, motility, and morphology.
What was found
Dutasteride and finasteride significantly suppressed serum DHT compared with placebo (dutasteride: -94%; finasteride: -73%; P < 0.001) and transiently increased serum testosterone. Total sperm count compared to baseline significantly decreased at 26 weeks (dutasteride: -28.6%; finasteride: -34.3%), but reductions were not statistically significant at 52 weeks (dutasteride: -24.9%; finasteride: -16.2%) or at 24-week follow-up (dutasteride: -23.3%; finasteride: -6.2%). At 52 weeks, semen volume was decreased (dutasteride: -29.7%, significant; finasteride: -14.5%, not significant) and sperm concentration showed non-significant decreases (dutasteride: -3.2%; finasteride: -7.4%). Both treatments caused a significant 6% to 12% reduction in sperm motility during treatment and at follow-up. Neither drug affected sperm morphology.
Why it matters
This study provides randomized evidence that 5alpha-reductase inhibition causes mild, largely reversible declines in sperm count, semen volume, and motility in healthy men without altering sperm morphology.
Limits
The study had a modest sample size (n = 99 across three arms) and evaluated only healthy men, limiting generalizability to men with pre-existing subfertility or oligospermia. Actual clinical fertility and pregnancy rates were not assessed, and sperm motility remained reduced through the 24-week recovery period.
Cited by
- supports Inhibiting DHT via 5-alpha reductase inhibitors can mildly suppress male fertility metrics because intratesticular DHT contributes to spermatogenesis.
- supports Dutasteride administration results in near-complete inhibition of systemic DHT levels.