Potential Side Effects of Finasteride
Finasteride commonly causes sexual side effects including decreased libido, erectile dysfunction, and ejaculatory dysfunction, which are typically reversible upon discontinuation of the medication but may persist in some patients. 1, 2
Primary Sexual Side Effects
Finasteride is associated with several sexual side effects that occur at higher rates than placebo:
- Decreased libido: 6.4% in year 1, decreasing to 2.6% in years 2-4 2
- Erectile dysfunction: 8.1% in year 1, decreasing to 5.1% in years 2-4 2
- Decreased ejaculate volume: 3.7% in year 1, decreasing to 1.5% in years 2-4 2
- Ejaculatory dysfunction: 0.8% in year 1, decreasing to 0.2% in years 2-4 2
These sexual side effects typically show a pattern of higher incidence during the first year of treatment with a decrease in subsequent years, suggesting some adaptation over time 1. However, they remain statistically significant compared to placebo even with continued use.
Other Common Side Effects
Beyond sexual dysfunction, finasteride can cause:
- Gynecomastia (breast enlargement): 0.5% in year 1, increasing to 1.8% in years 2-4 2
- Breast tenderness: 0.4% in year 1, increasing to 0.7% in years 2-4 2
- Rash: 0.5% in year 1, continuing at 0.5% in years 2-4 2
Effect on PSA Levels
An important clinical consideration with finasteride is its effect on PSA (Prostate Specific Antigen) levels:
- Reduces serum PSA by approximately 50% within 6 months of treatment 2
- For PSA monitoring in men taking finasteride for 6+ months, PSA values should be doubled for comparison with normal ranges 2
- A new PSA baseline should be established at least 6 months after starting treatment 2
Risk of High-Grade Prostate Cancer
The Prostate Cancer Prevention Trial (PCPT) found:
- Higher incidence of Gleason score 8-10 prostate cancer in men treated with finasteride (1.8%) compared to placebo (1.1%) 2
- This finding remains controversial as it may be due to detection bias rather than true biological effect 1
Discontinuation Rates
- Overall discontinuation rates for finasteride and placebo are approximately 15% 1
- Discontinuation specifically due to adverse events is approximately 6-7% 1
- In the FDA drug label study, 3.7% of patients on finasteride discontinued due to sexual side effects compared to 2.1% on placebo 2
Special Considerations
Post-Finasteride Syndrome
Some studies report persistent sexual side effects even after discontinuation of finasteride in a subset of patients, sometimes referred to as "post-finasteride syndrome" 3. However, this remains controversial with varying reports in the literature.
Topical Formulation Alternative
For patients concerned about systemic side effects, topical finasteride may be an alternative:
- Similar efficacy to oral formulation in some studies
- Reduced systemic absorption and potentially fewer sexual side effects
- Side effects are primarily localized to application site (pruritus, burning, irritation) 4
Contraindications
Finasteride is contraindicated in:
- Pregnant women or women who may become pregnant due to risk of abnormal development of male fetus genitalia 2
- Pediatric patients 2
Clinical Monitoring Algorithm
Before starting finasteride:
- Establish baseline PSA level
- Discuss potential side effects, particularly sexual dysfunction
- Rule out prostate cancer if clinically indicated
During treatment:
- Monitor for sexual side effects at each visit
- Establish new PSA baseline after 6 months
- Double PSA values for comparison with normal ranges
- Investigate any confirmed increase from lowest PSA value while on finasteride
If side effects occur:
- For mild sexual side effects: Reassure patient they may diminish over time
- For persistent or bothersome side effects: Consider discontinuation
- For gynecomastia: Evaluate and consider discontinuation if bothersome
After discontinuation:
- Sexual function typically returns to normal
- PSA levels will return to pre-treatment values within weeks
The decision to continue finasteride despite side effects should weigh the benefits (reduced risk of BPH progression, hair loss prevention) against the impact of side effects on quality of life.