How Finasteride Reduces Facial Hair
Finasteride reduces facial hair by inhibiting the enzyme 5-alpha-reductase type II, which blocks the conversion of testosterone to dihydrotestosterone (DHT) in hair follicles, thereby decreasing the androgenic stimulation that drives excessive hair growth in hirsutism. 1, 2
Mechanism of Action
Finasteride is a competitive and specific inhibitor of type II 5-alpha-reductase, the enzyme that metabolizes testosterone to DHT in the skin, prostate, and liver 1
By blocking this conversion, finasteride reduces local DHT concentrations in hair follicles by approximately 70%, which directly decreases the androgenic drive for terminal hair growth 1, 2
The drug forms a stable enzyme complex with 5-alpha-reductase, with extremely slow turnover (half-life ~30 days), providing sustained inhibition 1
Importantly, finasteride has no affinity for the androgen receptor itself—it works purely by reducing DHT production rather than blocking androgen action directly 1
Clinical Evidence in Hirsutism
In women with idiopathic hirsutism treated with finasteride 5 mg daily for 6 months, the Ferriman-Gallwey hirsutism score decreased significantly from 11.7 to 5.9 (approximately 50% reduction) 2
Serum DHT and 3-alpha-androstanediol glucuronide (a marker of peripheral 5-alpha-reductase activity) levels decreased significantly during treatment, confirming the biochemical mechanism 2
A randomized trial comparing finasteride to spironolactone found that finasteride reduced anagen hair diameter by 14% and Ferriman-Gallwey scores by approximately 2 points after 6 months 3
Topical finasteride cream (0.25%) applied to facial areas reduced hair counts from 27.5 to 15.5 per cm² (44% reduction) and decreased hair thickness significantly compared to placebo-treated sites 4
Hormonal Changes
Serum testosterone levels typically increase by 10-20% during finasteride treatment because less testosterone is being converted to DHT, but levels remain within the physiologic range 1, 2
The testosterone/DHT ratio increases significantly, reflecting the blocked conversion pathway 2, 3
Urinary 5-beta/5-alpha steroid metabolite ratios increase, indicating reduced 5-alpha-reductase activity systemically 2
Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) may increase by approximately 10%, but remain within normal ranges, and the hypothalamic-pituitary-gonadal axis remains intact 1
Clinical Efficacy Timeline
Maximum DHT suppression occurs approximately 8 hours after the first dose, with sustained suppression maintained throughout the 24-hour dosing interval 1
Clinical improvement in hirsutism becomes apparent after 3 months of treatment, with maximal benefit typically observed at 6 months 2, 5
Hair diameter reduction and decreased hair counts continue to improve throughout the 6-month treatment period 3, 4
Comparative Effectiveness
Finasteride demonstrates efficacy similar to spironolactone (100 mg daily) in reducing hirsutism scores and hair diameter, with both treatments producing approximately 13-14% reduction in hair diameter 3
Finasteride lowered hirsutism scores by 30-60% in most clinical trials, comparable to other antiandrogens but with fewer adverse effects 6
Combination therapy with oral contraceptives may produce slightly more pronounced clinical efficacy than finasteride monotherapy 2
Important Caveats
Finasteride is absolutely contraindicated in pregnancy due to teratogenic effects on male fetal genital development—women of childbearing potential must use reliable contraception 6
The drug should not be handled by pregnant women, as it can be absorbed through the skin 6
Sexual side effects (decreased libido) are less common in women than in men, but should still be discussed 2, 5
Long-term safety data beyond 6 months in women with hirsutism are limited, making it a secondary treatment option compared to first-line therapies like oral contraceptives or spironolactone 6
Clinical improvement is gradual and requires at least 3-6 months of continuous treatment to assess efficacy 2, 5