A pharmaceutical company reportedly sought to find the smallest effective quantity of finasteride and test its long-term effects on 1,553 men between ages 18 and 41 with mild to moderate thinning hair. Based on their research, 1 mg. daily was selected, and after two years of daily treatment, over 83% of the 1,553 men experiencing male hair loss had actually maintained or increased their hair count from baseline. Visual assessments concluded that over 80% had improved appearances.

Finasteride, marketed as the brand-name drug Propecia and Proscar by Merck, belongs to a class of drugs called aza-steroids. Finasteride is a “DHT inhibitor” and was originally approved by the FDA for the treatment of benign prostatic hyperplasia (BPH). It accomplishes this by blocking the production of 5-alpha-reductase, the enzyme responsible for the conversion of free testosterone to DHT. Propecia (1 mg of finasteride daily) blocks approximately 55% of DHT activity and Proscar (5mg of finasteride daily) blocks 70%. In 1997, Finasteride was approved by the FDA for the treatment of male pattern baldness. A 5 year study revealed that 9 of 10 men taking finasteride (1mg daily) experienced visible results (42% of men taking Propecia experienced no further hair loss while 48% experienced no further hair loss and hair regrowth). In clinical studies, finasteride, like Minoxidil, was shown to work on both the Crown (anatomy) area and the hairline area, but is most successful in the crown area.

Finasteride is usually only prescribed for men and should not even be touched by pregnant or potentially pregnant women, as it has been speculated that it could cause severe birth defects in male fetuses. Studies have shown that finasteride is ineffective for treating hair loss in women. However, finasteride’s supporters respond that the study was on post-menopausal women whose hairloss was more likely related to the loss of estrogen versus a sensitivity to testosterone. Other studies have shown that finasteride is effective for many women with follicular sensitivity to androgens.^{[citation needed]} Some doctors are now willing to prescribe finasteride to women on the condition that either the women is taking careful birth control measures or that the woman cannot become pregnant.