Finasteride: Recommended Use and Dosage
Benign Prostatic Hyperplasia (BPH)
For BPH, finasteride 5 mg daily is indicated specifically for men with documented prostatic enlargement (prostate volume >30cc) and lower urinary tract symptoms, and should not be used in men without prostatic enlargement. 1
Patient Selection Criteria
- Only prescribe finasteride for BPH patients with prostate volume greater than 30cc on imaging 1, 2
- Finasteride is ineffective and should not be used in men with LUTS who lack prostatic enlargement 1, 3, 2
- Greater clinical benefit occurs in men with larger prostates and/or higher PSA values 1, 3
Dosing and Administration
- Standard dose: 5 mg once daily 4, 5
- Symptom improvement takes several months; counsel patients that onset is slower than alpha-blockers 1
- Treatment should continue long-term, as studies demonstrate sustained benefit for 6-10 years 1, 3
Expected Clinical Outcomes
- Average 3-point improvement in AUA Symptom Index (considered clinically meaningful) 1, 3, 2
- 15-25% reduction in prostate size within 6 months 1, 3, 2
- Increased peak urinary flow rate 1
- Reduced risk of acute urinary retention and need for BPH-related surgery 4, 2
Combination Therapy Considerations
- Combination with an alpha-blocker provides superior symptom relief compared to finasteride monotherapy, particularly for patients with very large prostates or severe symptoms 1, 3, 2
- Consider combination therapy as first-line for patients requiring immediate symptom relief 3, 2
Critical PSA Monitoring Adjustments
- After 12 months of finasteride therapy, multiply the measured PSA value by 2 when screening for prostate cancer 4, 1, 3, 2
- Finasteride reduces PSA by approximately 50% after one year 4, 1, 3, 2
- Failure to adjust PSA interpretation is a common and serious pitfall that can delay prostate cancer diagnosis 1, 3, 2
Adverse Effects Profile
- Decreased libido: 6.4% in first year, decreasing to 2.6% in years 2-4 1
- Ejaculatory dysfunction: 3.7% in first year, decreasing to 1.5% in years 2-4 1
- Gynecomastia: 4.5% with long-term use 4
- Sexual side effects typically decrease after the first year and are reversible 1
- Overall discontinuation rate due to adverse events is approximately 6-7% 4
Androgenetic Alopecia (Male Pattern Baldness)
For male pattern hair loss, finasteride 1 mg daily is the FDA-approved dose and represents the first oral pharmacologic therapy for this condition. 6, 7
Dosing and Administration
- Standard dose: 1 mg once daily 8, 6, 7
- Long-term use (up to 5 years) has been studied in placebo-controlled trials with maintained efficacy 6
Mechanism and Efficacy
- Inhibits type 2 5α-reductase, preventing conversion of testosterone to dihydrotestosterone (DHT) 7
- Reduction in DHT results in significant improvement in hair growth and density 7
- Well-tolerated with favorable adverse event profile 6, 7
Adverse Effects
Critical PSA Monitoring for Hair Loss Patients
- Men aged 40-60 years taking 1 mg finasteride for hair loss experience a 40-50% reduction in PSA within 48 weeks 8
- The same PSA adjustment recommendation (multiply by 2) used for 5 mg BPH dosing should also apply to men taking 1 mg for androgenetic alopecia when screening for prostate cancer 8
- For men aged 40-49 years: median 40% PSA decrease 8
- For men aged 50-60 years: median 50% PSA decrease 8
Common Pitfalls to Avoid
- Do not prescribe finasteride for BPH in patients without documented prostatic enlargement (>30cc)—it will be ineffective 1, 3, 2
- Do not expect rapid symptom improvement; allow at least 6 months to assess effectiveness 1, 3
- Always double the PSA value after 12 months of therapy (regardless of dose) when screening for prostate cancer 4, 1, 3, 2, 8
- Do not discontinue prematurely due to sexual side effects without counseling patients that these effects typically diminish after the first year 1