Can finasteride (5-alpha-reductase inhibitor) cause low semen volume or quality?

Finasteride's Effects on Semen Volume and Quality

Finasteride at 5 mg/day is associated with reduced semen volume, while the evidence for the 1 mg/day dose used for hair loss is less conclusive regarding semen parameters. 1

Impact on Semen Parameters

Established Effects

• Semen Volume: The FDA label clearly states that treatment with finasteride for 24 weeks in healthy male volunteers showed a 0.6 mL (22.1%) median decrease in ejaculate volume 2
• This reduction in ejaculate volume is accompanied by a concomitant reduction in total sperm per ejaculate 2
• These changes remain within normal range and are generally reversible upon discontinuation of therapy, with an average time to return to baseline of 84 weeks 2

Dose-Dependent Effects

• The 5 mg/day dose (used for BPH) has more consistent evidence showing reduced semen volume 1
• For the 1 mg/day dose (used for male pattern baldness), the evidence is less conclusive:
  • Some studies report no significant effects on sperm concentration, total sperm per ejaculate, motility, or morphology 3
  • Other studies report temporary worsening of total sperm number and abnormal forms at 6 months of treatment 4

Fertility Implications

Reported Cases

• The FDA label acknowledges postmarketing reports of male infertility and/or poor seminal quality in men taking finasteride 2
• Case reports describe:
  • Improvement of semen parameters after discontinuation in men with pre-existing oligospermia 5
  • Secondary infertility associated with sperm DNA damage that improved after discontinuation 6

Risk Factors

• Men with pre-existing impaired spermatogenesis may be more vulnerable to further decreases in sperm parameters when taking finasteride 5
• The drug may have more significant impact in men who already have borderline fertility issues

Mechanism of Action

Finasteride works by:

• Inhibiting 5-alpha-reductase enzyme, preventing conversion of testosterone to dihydrotestosterone (DHT)
• DHT acts as primary androgen in prostate and hair follicles 7
• The reduction in ejaculate volume is likely related to finasteride's effects on prostate size and secretory function

Recommendations for Men Concerned About Fertility

1. For men actively trying to conceive:

   • Consider discontinuation of finasteride if fertility issues arise
   • Allow sufficient time (up to 84 weeks) for complete reversal of effects 2

2. For men with pre-existing fertility issues:

   • Exercise caution when using finasteride, especially at higher doses
   • Consider baseline semen analysis before starting therapy

3. For men on long-term therapy:

   • Be aware that normalization or improvement of seminal quality has been reported after discontinuation 2

Important Caveats

• Most studies show that while finasteride causes reductions in semen parameters, these typically don't fall below threshold levels that would interfere with fertility in men with normal baseline parameters 7
• The American Urological Association notes that finasteride at 5 mg/day is associated with reduced semen volume, but data for the 1 mg/day dose are inconclusive 1
• Sexual side effects (including reduced ejaculate volume) are consistently higher with finasteride than placebo, though the absolute magnitude is small (2-4% increase in reported events) 1

In summary, finasteride can reduce semen volume and potentially affect other semen parameters, particularly at the 5 mg dose. These effects are generally reversible upon discontinuation but may be more significant in men with pre-existing fertility issues.