Finasteride

Finasteride works by blocking 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT) — a more potent androgen responsible for prostate growth and scalp hair miniaturization ^[1][2].

Specifically, finasteride selectively inhibits the type II isoenzyme of 5-alpha reductase, which is predominantly found in the prostate gland, seminal vesicles, liver, and hair follicles ^[1]. (The type I isoenzyme, found mainly in skin and liver, is not significantly inhibited by finasteride but is targeted by dutasteride, which inhibits both isoforms.)

At the 5 mg dose (Proscar), finasteride reduces serum DHT levels by approximately 70% and intraprostatic DHT by about 80-90% ^[2]. This reduction causes the androgen-dependent prostatic epithelial cells to undergo apoptosis (programmed cell death), leading to gradual prostatic shrinkage of approximately 20-30% over 6-12 months ^[3]. This reduces the physical compression of the urethra that causes BPH symptoms.

At the 1 mg dose (Propecia), finasteride reduces scalp DHT sufficiently to halt the miniaturization of hair follicles in androgenetic alopecia (male pattern baldness) ^[4]. DHT normally causes susceptible hair follicles to progressively shrink, producing thinner, shorter hairs until the follicle becomes dormant. By reducing DHT, finasteride can stop this process and, in many men, partially reverse it.

Importantly, finasteride does not significantly affect testosterone levels — testosterone may actually increase slightly due to the blocked conversion pathway ^[1].

Finasteride requires patience — this is not a fast-acting medication.

For BPH (5 mg): Improvement in urinary symptoms typically begins at 3-6 months and continues to improve over 12 months ^[1]. Unlike tamsulosin which works in days, finasteride gradually shrinks the prostate. Your doctor may prescribe both initially for combined benefit.

For hair loss (1 mg): You may notice reduced hair shedding within 3 months and visible regrowth at 6-12 months ^[4]. Some men experience temporary increased shedding during the first few weeks as miniaturized hairs are replaced — this is not a reason to stop.

Sexual side effects (decreased libido, erectile dysfunction, reduced ejaculate volume) occur in approximately 3-8% of men ^[1]. These effects are dose-dependent and typically reverse after discontinuation, though a small number of men report persistent effects (see "post-finasteride syndrome" discussion in FAQs).

PSA monitoring: Finasteride reduces PSA levels by approximately 50%. Your doctor must account for this when interpreting PSA tests for prostate cancer screening ^[1].

Food: Finasteride can be taken with or without food ^[1]. Food does not affect absorption or efficacy.

Alcohol: No specific interaction between finasteride and alcohol ^[1]. Moderate alcohol consumption does not affect finasteride's efficacy. However, excessive alcohol can worsen urinary symptoms in BPH patients and contribute to hormonal imbalances.

Soy and Phytoestrogens: Some patients on internet forums discuss soy and phytoestrogen interactions with finasteride. There is no evidence of a clinically meaningful interaction ^[2].

BPH (Proscar): 5 mg orally once daily ^[1]. Can be used alone or in combination with an alpha-blocker (tamsulosin, doxazosin). The MTOPS trial showed the combination reduced clinical progression better than either agent alone over 4.5 years ^[3].

Male Pattern Hair Loss (Propecia): 1 mg orally once daily ^[4]. Treatment must be continued indefinitely — hair loss resumes within 12 months of discontinuation. Response should be assessed at 12 months.

No dose adjustment is required for renal impairment. Use with caution in hepatic impairment (decreased metabolism may increase drug levels) ^[1].

PSA Adjustment: After 6 months of finasteride therapy, multiply the measured PSA value by 2 to estimate the true PSA for cancer screening purposes ^[1]. Any confirmed increase in PSA during finasteride therapy should be evaluated, even if still in the "normal" range.

Duration: For BPH, finasteride is typically used long-term. For hair loss, it must be continued indefinitely to maintain results.

Generic finasteride is widely available at very low cost. A 30-day supply of finasteride 1 mg (for hair loss) costs approximately $5-15, and 5 mg (for BPH) costs $4-10 at most pharmacies ^[5].

Cost-saving strategies: - Generic is standard: Both Proscar and Propecia patents have expired. Generic finasteride is FDA "AB" rated - $4 generic lists: Finasteride 5 mg is on most pharmacy discount programs. The 1 mg may or may not be included - Pill splitting (with doctor approval): Some patients prescribed 1 mg for hair loss split the 5 mg tablet (which is cheaper) into quarters using a pill splitter. This is an off-label practice that should only be done with physician guidance - GoodRx coupons: Can reduce costs to $3-8 for a 30-day supply - Avoid brand Propecia: No clinical advantage over generic. Propecia costs $60-90/month vs. $5-15 generic - No insurance coverage for hair loss: Most insurance does not cover finasteride for cosmetic hair loss, but it is covered for BPH diagnosis

Pregnancy (Category X): Finasteride is absolutely contraindicated in pregnancy and in women who may become pregnant ^[1]. It can cause abnormal genital development (ambiguous genitalia) in male fetuses by blocking the DHT production essential for normal male sexual differentiation.

Handling Warning: Women who are or may become pregnant should not handle crushed or broken finasteride tablets because the drug can be absorbed through the skin ^[1]. Intact tablets have a coating that prevents skin absorption during normal handling.

Exposure Through Semen: Finasteride is present in semen at concentrations approximately 50-100 times lower than the dose that could affect fetal development. The risk from exposure through semen is considered negligible, and use of condoms is not specifically required, though some clinicians recommend it during the first trimester of a partner's pregnancy ^[1].

Breastfeeding: Not applicable — finasteride is not approved for use in women.

Male Fertility: Finasteride can reduce sperm count and motility in some men (by 20-30%), though most remain in the normal range. Effects are reversible upon discontinuation ^[1].

Both Proscar (5 mg) and Propecia (1 mg) patents have expired, and generic finasteride is now the standard dispensed product.

Generic finasteride is available from numerous manufacturers in both 1 mg and 5 mg tablets, all FDA "AB" rated as therapeutically equivalent to the brand products.

The price differential is dramatic: - Propecia (1 mg): $60-90/month - Generic finasteride 1 mg: $5-15/month - Proscar (5 mg): $80-120/month - Generic finasteride 5 mg: $4-10/month

There is no clinical reason to use brand-name finasteride.