What is the incidence of erectile dysfunction with Finasteride (Dutasteride/5-alpha-reductase inhibitor)?

Incidence of Erectile Dysfunction with Finasteride

The incidence of erectile dysfunction with finasteride ranges from 8.1% in the first year to 18.5% in longer-term studies, compared to 3.7-14.4% with placebo, representing an absolute increase of approximately 2-4% over placebo. 1

Time-Dependent Incidence Patterns

The incidence of erectile dysfunction varies significantly based on treatment duration:

First Year of Treatment

• Erectile dysfunction occurs in 8.1% of finasteride users versus 3.7% of placebo users in the 4-year Long-Term Efficacy and Safety Study, representing a 4.4% absolute increase 1
• In mid-term studies (1-2 years), rates range from 4.2% to 15.8% depending on the study population 2, 3
• The MTOPS study reported 18.5% with finasteride monotherapy versus 12.2% with placebo 1

Years 2-4 of Treatment

• The incidence equalizes to 5.1% in both finasteride and placebo groups, with no significant difference between treatment groups 1
• This convergence suggests that sexual side effects decrease over time with continued treatment 3

Clinical Context and Magnitude

The clinical significance of finasteride-induced erectile dysfunction is modest: on a 0-100 scale measuring sexual dysfunction, finasteride causes a mean difference of only 3.21 points, compared to 1.26 points for each additional year of age. 4, 3

Discontinuation Rates

• Only 3.7% of patients discontinued finasteride due to sexual side effects versus 2.1% with placebo 1
• Overall discontinuation rates are approximately 15% in both finasteride and placebo groups 4, 3
• Discontinuation specifically due to adverse events is 6-7% in both treatment and placebo groups 4, 3

Population-Specific Considerations

BPH Treatment (5 mg dose)

• Higher rates of erectile dysfunction are consistently reported in BPH populations, with most studies showing correlation between finasteride and ED 5
• The PCPT trial reported 67.4% cumulative incidence over 7 years versus 61.5% with placebo (relative risk 1.10), though this includes baseline sexual dysfunction in an older population 2

Male Pattern Hair Loss (1 mg dose)

• Most studies reveal that finasteride for androgenetic alopecia is not correlated with ED 5
• However, the 1 mg dose produces similar PSA suppression (50% decrease at 1 year) as the 5 mg dose in men over 50 years 2

Nocebo Effect

A significant nocebo effect influences reported rates: patients counseled about sexual side effects reported 43.6% incidence versus 15.3% in those not informed (P=0.03). 6

• Erectile dysfunction was reported in 30.9% of informed patients versus 9.6% of uninformed patients (P=0.02) 6
• This nocebo burden must be considered when interpreting clinical practice rates versus controlled trial data 6

Persistent Sexual Dysfunction

The FDA amended finasteride labels to warn about persistent symptoms after discontinuation, though this is based on anecdotal patient reports rather than prospective trials. 3, 1

• Post-marketing reports describe persistent sexual dysfunction in some patients, with one study reporting symptoms lasting a mean of 40 months after discontinuation 7
• Post-finasteride syndrome remains poorly defined and controversial, with unclear data quality supporting its existence 4
• In one clinical series, 96% of subjects with persistent sexual side effects (≥3 months) continued to experience dysfunction at 14-month reassessment 8

Critical Caveats

When interpreting erectile dysfunction rates, clinicians must account for:

• Baseline sexual dysfunction is common in BPH populations: 46% of men in the PLESS study had a history of sexual dysfunction at screening 2
• Age-related sexual dysfunction increases independently of medication use 4, 3
• The PCPT study population (mean age 62-65 years) had high baseline rates of sexual dysfunction 2
• Disproportionality in adverse event reporting is strongest in men aged 31-45 years 9