Will Finasteride Reduce Ejaculate Volume?
Yes, finasteride will reduce the volume of semen you ejaculate, though the decrease is modest and does not interfere with normal sexual function or fertility in most men. 1
Magnitude of Ejaculate Volume Reduction
The FDA label explicitly states that ejaculate volume may decrease in some patients during finasteride treatment, though this does not appear to interfere with normal sexual function. 1
At the 5 mg dose (used for prostate enlargement), ejaculate volume decreases by approximately 25%. 2
At the 1 mg dose (used for hair loss), the reduction is much smaller—only about 11% compared to 8% with placebo, representing a clinically insignificant difference of approximately 0.03 ml. 2
Reduced ejaculate volume is reported in 1.5–7.2% of patients, representing a 2.6-fold increased risk versus placebo. 3
Mechanism Behind the Effect
Finasteride inhibits the 5-alpha-reductase enzyme, which converts testosterone to dihydrotestosterone (DHT). Since DHT plays a role in prostate and seminal vesicle function, blocking its production reduces the contribution of these glands to semen volume. 4, 5
The prostate gland shrinks by approximately 20% with finasteride treatment, which directly contributes to decreased ejaculate production. 4, 2
Impact on Fertility and Sexual Function
Despite the volume reduction, finasteride at 1 mg daily does not affect sperm concentration, total sperm per ejaculate, sperm motility, or morphology in young men. 2
The 2024 American Urological Association/American Society for Reproductive Medicine guidelines state that finasteride 1 mg/day has inconclusive evidence regarding fertility impact, while the 5 mg dose is associated with reduced semen volume. 6
Reduction in ejaculatory volume is the only established causal relationship between finasteride and sexual dysfunction—it does not directly impair erectile function or libido through this mechanism. 5
Clinical Context and Reversibility
The decrease in ejaculate volume is reversible upon discontinuation of finasteride. 2
For men undergoing post-cycle therapy to restore fertility, finasteride should be discontinued for the entire duration of the protocol because continuing a drug that impairs semen volume directly opposes the therapeutic goal. 6
Overall discontinuation rates due to adverse events are approximately 6–7% in both finasteride and placebo groups, indicating that most men tolerate the ejaculate volume reduction without significant concern. 3, 7
Key Caveat
The reduction in ejaculate volume is dose-dependent: men taking 1 mg for hair loss experience minimal change (essentially equivalent to placebo), while men taking 5 mg for prostate enlargement experience a more noticeable 25% reduction. 2 This distinction is critical when counseling patients about what to expect based on their prescribed dose.