Side Effects of Finasteride (Propecia)
Finasteride commonly causes sexual side effects including decreased libido, ejaculatory dysfunction, and erectile dysfunction, which are reversible upon discontinuation but may persist in some patients after stopping the medication. 1, 2
Common Side Effects
Sexual Side Effects
- Erectile dysfunction: Occurs in 8.1% of patients in the first year (vs 3.7% with placebo) 2
- Decreased libido: Affects 6.4% of patients in the first year (vs 3.4% with placebo) 2
- Decreased ejaculate volume: Reported in 3.7% of patients in the first year (vs 0.8% with placebo) 2
- Ejaculation disorders: Occurs in 0.8% of patients in the first year (vs 0.1% with placebo) 2
These sexual side effects tend to decrease over time but remain statistically significant compared to placebo. In years 2-4 of treatment, erectile dysfunction and decreased libido rates equalize with placebo (5.1% and 2.6% respectively), while ejaculation disorders remain more common with finasteride 2.
Endocrine Effects
- Breast enlargement (gynecomastia): 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
Other Side Effects
- Rash: 0.5% in year 1, continuing at similar rates in years 2-4 2
Post-Marketing Reports
The FDA label reports additional adverse events identified during post-marketing surveillance 2:
- Hypersensitivity reactions: Including pruritus, urticaria, and angioedema
- Testicular pain
- Hematospermia (blood in semen)
- Persistent sexual dysfunction: Some patients report sexual side effects that continue after discontinuation of treatment
- Male infertility/poor seminal quality: Reported rarely, with normalization after discontinuation
- Depression
- Male breast cancer: Rare cases reported
Effect on PSA Levels
Finasteride reduces serum PSA levels by approximately 50% after 12 months of therapy 1. This is clinically important because:
- PSA levels must be doubled when screening for prostate cancer in men taking finasteride
- Failure to account for this reduction could mask the detection of prostate cancer 1
Long-Term Effects and Discontinuation
- Approximately 3.7% of patients discontinue finasteride due to sexual side effects 2
- Most side effects are reversible upon discontinuation 1
- However, post-finasteride syndrome has been reported - a controversial condition involving persistent sexual, physical, and psychological symptoms after stopping the medication 1
- The FDA has added a warning about potential persistent sexual side effects to the drug label, though the evidence is based primarily on anecdotal reports rather than prospective trials 1
Risk Factors for Side Effects
- Age: Older men may experience more sexual side effects
- Dosage: The 5mg dose used for BPH has more reported sexual side effects than the 1mg dose used for hair loss, though the 1mg dose can still cause similar issues 3
- Duration of treatment: Sexual side effects may decrease over time but can persist in some patients 2
Clinical Considerations
- Discuss potential side effects with patients before initiating therapy
- Monitor for sexual dysfunction, breast changes, and mood alterations
- Consider the risk-benefit ratio, especially in patients with pre-existing sexual dysfunction
- Remember that discontinuation of finasteride will lead to reversal of therapeutic effects (prostate size reduction or hair growth) 4
- In geriatric patients, carefully weigh medication burden against benefits, as side effects may have greater impact on quality of life 5
Finasteride remains an effective treatment for BPH and male pattern baldness, but patients should be fully informed about potential side effects, particularly those related to sexual function, before starting treatment.