After one year of oral finasteride therapy, are sexual side effects still present?

Sexual Side Effects After One Year of Finasteride

Sexual side effects from finasteride do persist after one year of treatment, but the incidence of NEW sexual adverse events drops dramatically—becoming equivalent to placebo rates after the first year. 1, 2

Key Evidence on Temporal Pattern of Sexual Side Effects

The most robust data comes from the 4-year PLESS trial, which clearly demonstrates a temporal pattern:

Year 1:

• 15% of finasteride-treated patients experienced drug-related sexual adverse events versus 7% on placebo (statistically significant difference) 2
• Sexual side effects included erectile dysfunction (8.1% vs 3.7%), decreased libido (6.4% vs 3.4%), and decreased ejaculate volume (3.7% vs 0.8%) 3

Years 2-4:

• No significant difference between finasteride and placebo groups in the incidence of NEW sexual adverse events (7% in each group) 2
• This represents a critical finding: after the first year, patients continuing finasteride develop new sexual problems at the same rate as those on placebo 1, 2

Resolution Patterns

The evidence shows that sexual side effects can resolve even while continuing therapy:

• 12% of finasteride patients experienced resolution of sexual adverse events while continuing treatment (compared to 19% on placebo) 2
• Among those who discontinued due to sexual side effects, approximately 50% experienced resolution after stopping finasteride 2

Important Clinical Caveats

The Nocebo Effect is Substantial: A well-designed blinded study demonstrated that patients counseled about sexual side effects experienced them at significantly higher rates (43.6% vs 15.3%) compared to those not informed 4. When specifically told about erectile dysfunction, 30.9% reported it versus only 9.6% in the uninformed group 4. This suggests that a significant portion of reported sexual dysfunction may be attributable to expectation rather than direct pharmacological effect.

Magnitude of Effect: Even when statistically significant, the clinical magnitude was modest. In the PCPT trial, the largest effect of finasteride on sexual functioning was a mean difference of 3.21 points on a 0-100 scale—comparable to the effect of 2.5 years of aging (1.26 points per year) 1.

Discontinuation Rates: Only 3.7% of finasteride patients versus 2.1% of placebo patients discontinued therapy due to sexual adverse events over 4 years 2. This low discontinuation rate suggests that for most patients, sexual side effects are either tolerable, resolve, or are not severe enough to warrant stopping treatment.

Clinical Algorithm for Counseling

At initiation:

• Inform patients that sexual side effects occur most commonly in the first year (approximately 8% excess risk over placebo)
• Emphasize that NEW sexual problems after year 1 occur at the same rate as placebo
• Acknowledge the substantial nocebo effect to help patients contextualize symptoms

During follow-up:

• If sexual side effects develop in year 1: Consider continuing therapy as symptoms may resolve spontaneously (occurred in 12% of patients) 2
• If symptoms persist beyond 1 year: Reassess whether they represent true drug effect versus other factors (aging, comorbidities, nocebo)
• If discontinuation is chosen: Inform that approximately 50% experience resolution after stopping 2

The evidence clearly shows that while sexual side effects are more common with finasteride than placebo during the first year, this increased risk does not persist into subsequent years of treatment 1, 2.