What percentage of patients taking Proscar (finasteride) experience erectile dysfunction?

Erectile Dysfunction Rates with Proscar (Finasteride)

Approximately 8.1% of patients taking Proscar (finasteride) experience erectile dysfunction in the first year of treatment, compared to 3.7% on placebo, representing an absolute drug-attributable increase of 4.4%. 1, 2

Year-by-Year Breakdown

First Year of Treatment:

• Impotence/erectile dysfunction occurs in 8.1% of finasteride-treated patients versus 3.7% on placebo 1, 2
• This represents the highest risk period for developing sexual side effects 1
• The absolute increase attributable to finasteride is approximately 4.4% 1

Years 2-4 of Treatment:

• The incidence equalizes to 5.1% in both finasteride and placebo groups, with no significant difference between treatments 1, 2
• New sexual adverse events occur in only 7% of both finasteride and placebo groups during this period 3

Important Clinical Context

Baseline Sexual Dysfunction:

• 46% of men in clinical trials had pre-existing sexual dysfunction at baseline, making attribution to finasteride challenging in individual cases 1, 3
• Men with or without baseline sexual dysfunction showed similar drug-related sexual adverse event profiles 3

Discontinuation Rates:

• Only 3.7% of finasteride patients discontinued therapy due to sexual adverse reactions (versus 2.1% on placebo) 2
• Among those who discontinued, approximately 50% experienced resolution of sexual dysfunction after stopping finasteride 3

Resolution While Continuing Therapy:

• 12% of finasteride patients experienced resolution of sexual adverse events while continuing treatment (compared to 19% on placebo) 3

Critical Caveats

Nocebo Effect:

• The nocebo phenomenon significantly inflates reported rates in clinical practice 4
• Patients informed about sexual side effects reported 43.6% incidence versus 15.3% in uninformed patients taking the same medication 4
• This explains the discrepancy between controlled trial data (8.1%) and higher rates sometimes reported in clinical practice 4

Duration-Dependent Risk:

• Longer exposure (>205-208 days) may increase risk of persistent erectile dysfunction that continues after discontinuation 5
• Among men who developed erectile dysfunction on finasteride, 31.5% experienced persistent dysfunction lasting beyond 90 days after stopping the medication 5

Magnitude of Effect:

• The sexual dysfunction effect is relatively modest, causing a mean difference of 3.21 points on a 0-100 scale compared to placebo 1
• This is approximately 2.5 times the annual effect of natural aging (1.26 points per year) 1