Finasteride for Gender-Affirming Care: Off-Label Use, Dosing Protocol, and Evidence Review

Does finasteride have an approved use in gender-affirming care?

No. The 1 mg tablet (Propecia) is indicated for male pattern hair loss in men only and is not indicated for use in women [1]. The 5 mg tablet (Proscar) is indicated for symptomatic benign prostatic hyperplasia in men with an enlarged prostate [2]. Neither label covers lowering DHT within a feminizing hormone regimen. A 2013 JAMA clinical review lists finasteride among medications used in male-to-female hormone treatment, a description of practice rather than a trial [3].

What finasteride does to DHT

Finasteride is a competitive, specific inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to DHT, with about 100-fold selectivity over type I; type II accounts for roughly two-thirds of circulating DHT [1]. One 1 mg tablet suppresses serum DHT by 65% within 24 hours [1]. Mean testosterone and estradiol each rose by about 15% and stayed within the physiologic range, and finasteride has no affinity for the androgen receptor [1].

Is there a dosing protocol?

The FDA labels give doses only for their approved uses. The Propecia label says one 1 mg tablet once daily, with or without food, and that daily use for three months or more is generally necessary before benefit is observed in hair loss; it also says withdrawal of treatment leads to reversal of effect within 12 months [1]. The Proscar label says 5 mg once daily for BPH [2]. Neither label gives a dose, DHT target or outcome measure for gender-affirming care.

Finasteride 1 mg tablets are prescription-only [1]. HealthRX.com offers finasteride 1 mg.

What the label says to watch for

In three 12-month controlled trials of the 1 mg dose (945 men on finasteride, 934 on placebo), 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% vs 2.1% reported one or more (p=0.04) [1].

The postmarketing section lists sexual dysfunction that continued after discontinuation, depression, and suicidal ideation and behavior. The label states these reports are voluntary and that a causal relationship cannot reliably be established [1][4].

The Propecia label lists pregnancy as a contraindication and says women who are or may be pregnant should not handle crushed or broken tablets; intact coated tablets prevent contact during normal handling [1].

What is not known

The labeled trials enrolled men aged 18 to 41 with hair loss [1] and men aged 45 to 78 with BPH [2]. The labels contain no data on how far DHT falls, or on hair, skin or longer-term outcomes, in transgender or nonbinary adults taking finasteride with estradiol.