Why does Proscar (finasteride) take so long to show significant effects in treating benign prostatic hyperplasia (BPH) and androgenetic alopecia?

From the Guidelines

Proscar (finasteride) takes several months to show significant effects in treating benign prostatic hyperplasia (BPH) and androgenetic alopecia because of its mechanism of action, with noticeable improvements typically requiring 3-6 months and maximum benefits often requiring 6-12 months of continuous treatment. Finasteride works by inhibiting the enzyme 5-alpha reductase, which converts testosterone to dihydrotestosterone (DHT) 1. DHT is responsible for prostate enlargement in BPH and hair follicle miniaturization in male pattern baldness. When taking the standard dose of 5mg daily for BPH or 1mg daily for hair loss, patients typically need to wait for the medication to gradually reduce DHT levels, allowing for slow reversal of the underlying pathological processes. The medication must first lower DHT levels (which happens within days), but then physiological changes must follow - including gradual reduction in prostate tissue volume or the initiation of new hair growth cycles. Additionally, hair grows in cycles, so visible improvements in hair density require completion of these growth cycles. Patients should understand that consistent daily use is essential, and discontinuation will result in reversal of benefits within 6-12 months as DHT levels return to baseline.

Some key points to consider when treating patients with finasteride include:

• The reduction of DHT in prostate tissues has been measured at approximately 80% with finasteride 1
• Finasteride selectively inhibits the 5-AR type II isoenzyme, which is the primary enzyme responsible for converting testosterone to DHT in the prostate 1
• Patients should be counseled on the potential side effects of finasteride, including impotence, decreased libido, and gynecomastia 1
• The medication is most effective in patients with larger prostates and higher PSA values, and treatment should be tailored to the individual patient's needs 1

Overall, finasteride is a effective treatment for BPH and androgenetic alopecia, but patients must be patient and consistent with their treatment regimen to see significant improvements.

From the FDA Drug Label

Finasteride is a competitive and specific inhibitor of Type II 5α-reductase with which it slowly forms a stable enzyme complex. Turnover from this complex is extremely slow (t½ ~ 30 days). In patients treated for three months, prostate volume, which declined by approximately 20%, returned to close to baseline value after approximately three months of discontinuation of therapy.

The slow onset of action of Proscar (finasteride) can be attributed to the slow turnover of the finasteride-5α-reductase complex, with a half-life of approximately 30 days. This means that it takes time for the drug to reach its full effect, and similarly, it takes time for the effects to wear off after discontinuation of therapy. Additionally, the slow accumulation phase of finasteride after multiple dosing also contributes to the delayed onset of action. It may take several months of continuous treatment to achieve significant effects in treating benign prostatic hyperplasia (BPH) and androgenetic alopecia 2.

From the Research

Delayed Effects of Proscar (Finasteride)

The delayed effects of Proscar (finasteride) in treating benign prostatic hyperplasia (BPH) and androgenetic alopecia can be attributed to several factors:

• The mechanism of action of finasteride, which involves the inhibition of type 2 5alpha-reductase, leading to a decrease in dihydrotestosterone (DHT) levels 3, 4
• The time required for finasteride to reduce prostate volume and improve urinary symptoms, which can take several months to a few years 5, 6
• The variability in individual response to finasteride, with some patients experiencing significant improvements in symptoms and others showing minimal response 7

Factors Influencing Response to Finasteride

Several factors can influence the response to finasteride, including:

• Prostate size, with larger prostates tend to respond better to finasteride 7
• Duration of treatment, with longer treatment durations tend to result in greater improvements in symptoms 5, 7
• Individual variability in response to finasteride, with some patients experiencing significant improvements in symptoms and others showing minimal response 3, 4

Clinical Trial Results

Clinical trials have consistently shown that finasteride can reduce the risk of acute urinary retention and the need for surgical treatment among men with BPH 5, 7. Additionally, finasteride has been shown to improve urinary symptoms and reduce prostate volume in men with BPH 6, 7. In the treatment of androgenetic alopecia, finasteride has been shown to promote hair growth and prevent further hair loss in a significant proportion of men 3, 4.