Finasteride Dosing Strengths
Finasteride is available in two FDA-approved strengths: 1 mg for androgenetic alopecia (male pattern hair loss) and 5 mg for benign prostatic hyperplasia (BPH). 1
Approved Dosing by Indication
For Androgenetic Alopecia (Male Pattern Hair Loss)
- 1 mg daily is the approved and optimal dose for treating male pattern hair loss 2, 3
- This lower dose was specifically studied and approved for hair loss treatment in 1997 2
- Clinical trials demonstrated that 1 mg/day effectively grows hair in up to 66% of men with mild to moderate alopecia and prevents further hair loss in 91% of patients 4
- Long-term studies over 5 years confirmed sustained efficacy at this dose 3
For Benign Prostatic Hyperplasia (BPH)
- 5 mg daily is the approved dose for treating symptomatic BPH 1, 5
- This dose was the original formulation developed and approved in 1992 for BPH 2, 6
- The 5 mg dose reduces prostate volume by approximately 20%, improves urinary flow rate by about 3 mL/s, and reduces the risk of acute urinary retention and need for surgery 7, 5
- Can be used as monotherapy or in combination with alpha-blockers like doxazosin 1
Pharmacologic Rationale for Different Strengths
The dose-response relationship shows that doses below 0.5 mg/day produce minimal DHT suppression, while doses above 5 mg/day provide little additional benefit. 5
- Both 1 mg and 5 mg doses reduce serum DHT by approximately 70% 7, 1
- A single study demonstrated that 1 mg finasteride produces a similar 50% decrease in PSA levels as the 5 mg dose in men aged 50 years and older at 1-year follow-up 7
- The 5 mg dose reduces DHT in prostate tissue by approximately 80%, while dutasteride (which inhibits both type I and II 5α-reductase) reduces it by 94% 7
Clinical Considerations
For BPH treatment, finasteride 5 mg should be reserved for patients with documented prostatic enlargement (prostate volume >30cc, PSA >1.5 ng/mL, or palpable enlargement on DRE). 7
- The larger the prostate gland, the more pronounced the treatment effects 7
- Symptom improvement with 5-ARIs is slower compared to alpha-blockers, with maximal effects typically seen after 6-12 months 7
- Treatment duration of at least 7 years was studied in the Prostate Cancer Prevention Trial for cancer prevention, though this is not an approved indication 7
Important Safety Information
Patients must be counseled about sexual side effects (decreased libido, erectile dysfunction, ejaculatory dysfunction) which occur in 4-10% of patients, and gynecomastia which occurs in 0.5-2.2% of patients. 7, 8
- Sexual side effects are typically reversible after discontinuation 9
- PSA levels decrease by approximately 50% after 1 year of therapy; measured PSA values should be doubled when screening for prostate cancer in men taking finasteride 7
- The FDA has added warnings about post-finasteride syndrome, though the evidence supporting this remains controversial and based primarily on anecdotal reports rather than prospective trials 7