Inside the Olsen Finasteride 5-year Methodology: What Most Summaries Skip

What the five-year study actually was

The program began as two 1-year, double-blind, placebo-controlled trials in 1,553 men aged 18 to 41 with mild to moderate male pattern hair loss [2][4]. Hair count and patient self-assessment were the primary endpoints; investigator assessment and ratings of photographs were secondary [4].

Of the men who completed the first 12 months, 1,215 elected to continue, and the long-term report covers up to four 1-year extensions, five years in total [1]. The second-year extension was double-blind and placebo-controlled [2][4], and the long-term report describes all the extensions as placebo-controlled [1]. That is the structural point most write-ups miss: the placebo arm did not dissolve at month 12, and the long-term comparison is still finasteride against placebo. Men assigned to placebo showed progressive hair loss across the program [1].

How the hair was counted

The numeric endpoint was a hair count inside a 1-inch diameter circular area (5.1 cm2) of balding vertex scalp, starting from a baseline of 876 hairs [2]. Finasteride produced 107 more hairs than placebo at one year and 138 more at two years, P<0.001 [2]. Patient self-assessment, investigator assessment and photograph review moved in the same direction [2].

A single fixed circle is a narrow window. It captures the vertex and nothing else. A third trial in the same development program enrolled 326 men with mild to moderate hair loss in the anterior mid-scalp, with or without vertex balding [4], and the label states that efficacy in bitemporal recession has not been established [4]. The long-term numbers are vertex numbers.

The protocol detail almost no summary mentions

Every man in the trials, whether assigned to finasteride or placebo, was instructed to use a specified medicated tar-based shampoo (Neutrogena T/Gel) during the first two years, to prevent seborrheic dermatitis from confounding the assessment of hair growth [4]. The year 1 and year 2 hair counts were therefore generated under a standardized scalp-care protocol [4].

Dose and timing in the program

The trials used finasteride 1 mg once daily, with or without food [4]. The label says daily use for three months or more is generally necessary before benefit is observed, continued use is recommended to sustain benefit, and withdrawal of treatment leads to reversal of effect within 12 months [4].

No minoxidil arm

Placebo was the only comparator. A 1999 review of finasteride in male pattern hair loss stated that its clinical efficacy had not been compared with topical minoxidil [3]. A 2017 systematic review and meta-analysis pooled finasteride 1 mg and 5% minoxidil trials separately, each against placebo, and found both superior to placebo [5]. This program supports no claim that one drug beats the other over five years.

Safety over five years

In the three 12-month controlled trials, drug-related decreased libido was reported by 1.8% on finasteride versus 1.3% on placebo, erectile dysfunction by 1.3% versus 0.7%, and ejaculation disorder by 1.2% versus 0.7%; 3.8% versus 2.1% reported one or more of these (p=0.04), and 1.2% versus 0.9% discontinued for a drug-related sexual event [4]. The incidence of each of these reactions fell to 0.3% or less by the fifth year of treatment [4]. A self-administered sexual function questionnaire at month 12 showed statistically significant differences in favor of placebo in three of four domains (sexual interest, erections, and perception of sexual problems), with no significant difference in overall satisfaction with sex life [4].

The long-term report concluded that finasteride was generally well tolerated and that no new safety concerns emerged over five years [1]. Set against that, safety reporting across finasteride hair-loss trials has a known weakness. A 2015 meta-analysis of 34 trials found that none had adequate safety reporting, 76% evaluated safety for one year or less, and funnel plots suggested systematic under-detection of sexual adverse effects; only 31% of 5,704 men treated in practice would have met the entry criteria of the pivotal trials [6]. A 2019 meta-analysis of 15 randomized placebo-controlled trials (4,495 men) put the relative risk of sexual dysfunction at 1.66 with finasteride 1 mg (95% CI 1.20 to 2.30) [7].

The current Propecia label also lists, as postmarketing reports, sexual dysfunction that continued after discontinuation (erectile dysfunction, libido disorders, ejaculation disorders, orgasm disorders) plus male infertility and poor seminal quality, with the caveat that these voluntary reports come from a population of uncertain size and a causal relationship cannot reliably be established [4][8].

What five years of data does not settle

The report covers five years and does not describe follow-up beyond that [1]. It counts vertex hair, and the label's statement on bitemporal recession is a limitation rather than a result [4]. It also cannot say how often sexual side effects persist after stopping: the label lists persistence as a postmarketing report [4], and the most-cited interview study, 71 men with a mean 28 months of use and mean 40 months of persistence, was post hoc and self-selected and cannot produce a frequency [9].

Bottom line

For men like those enrolled, aged 18 to 41 with mild to moderate vertex loss, finasteride 1 mg daily produced hair counts above placebo at every reported time point through two years, with durable improvement versus placebo at five years, under placebo-controlled conditions and a standardized shampoo protocol [2][1][4]. The caveats are the vertex-only counting window, the absence of a minoxidil arm, and safety reporting across finasteride hair-loss trials that a 2015 meta-analysis judged inadequate [4][3][6]. HealthRX.com offers finasteride 1 mg by prescription.