Finasteride Microdosing Protocols: What the Evidence Actually Shows

What dose was actually tested?

The hair-loss evidence is built on 1 mg daily. In two 1-year placebo-controlled trials, 1,553 men aged 18 to 41 received finasteride 1 mg daily or placebo, and 1,215 continued into blinded extensions for a second year. Hair count in a 1-inch (5.1 cm2) circle of balding vertex scalp was 107 hairs above placebo at 1 year and 138 above at 2 years, while placebo-treated men kept losing hair (P<0.001) [2]. The label specifies one 1 mg tablet once daily, with or without food [1].

What lower doses were tested?

Two separate dose-ranging studies assigned men aged 18 to 36 with moderate vertex hair loss to finasteride 5, 1, 0.2 or 0.01 mg a day, or placebo. Efficacy was shown on all endpoints at 0.2 mg a day or higher; 1 mg and 5 mg had similar efficacy that was superior to the lower doses, and 0.01 mg was similar to placebo. No significant safety issues were identified, and 1 mg a day was chosen as the optimal dose [7].

Why a short half-life does not change the schedule

Finasteride leaves the blood quickly, with a mean terminal half-life of about 5 to 6 hours in men aged 18 to 60 and about 8 hours over 70, while the Type II enzyme complex it blocks turns over slowly, with a half-life of roughly 30 days [1]. The label's regimen is still one tablet daily [1], and alternate-day or split-tablet schedules are not part of it.

What are the side-effect rates?

The label's rates are for 1 mg. Across three 12-month controlled trials (945 men on finasteride, 934 on placebo, aged 18 to 41), drug-related decreased libido was 1.8% vs 1.3%, erectile dysfunction 1.3% vs 0.7%, and ejaculation disorder 1.2% vs 0.7%; 3.8% (36 of 945) reported one or more of these versus 2.1% (20 of 934) on placebo (p=0.04) [1]. A meta-analysis of 15 randomized placebo-controlled trials (4,495 men) put the relative risk of sexual dysfunction at 1.57 (95% CI 1.19 to 2.08), and 1.66 (1.20 to 2.30) for finasteride alone [5]. In the 4-year PLESS study of 1,524 men with BPH on finasteride 5 mg and 1,516 on placebo, year-1 impotence was 8.1% vs 3.7% and decreased libido 6.4% vs 3.4% [6].

What the label lists

The Propecia postmarketing section lists sexual dysfunction that continued after stopping, and depression, suicidal ideation and behavior, as voluntary reports from a population of uncertain size where a causal relationship cannot reliably be established; there is no boxed warning [1]. The Propecia label contraindicates use by women who are or may become pregnant, because finasteride may cause abnormal development of the external genitalia of a male fetus. Pregnant women should not handle crushed or broken tablets [1].

Bottom line

Drugs@FDA lists oral finasteride tablets in 1 mg and 5 mg strengths and no approved topical or injectable finasteride [3][4]. For hair loss, the labeled finasteride regimen is 1 mg once daily, and stopping reverses the effect within 12 months [1].