Answer:
Minoxidil was developed to treat hypertension. It is a potassium-channel opener and vasodilator. Its mechanism of action with respect to hair growth is unknown, but appears to be independent of vasodilatation. A 2% topical solution was approved by the FDA in 1988 for promoting hair growth in men with androgenetic alopecia (hereditary thinning of the hair induced by androgens). A 12-month placebo-controlled study of 2294 men documented significantly increased hair counts and an increase in the diameter of the hair shaft. In 1997, a 5% topical solution was approved by the FDA as an over-the-counter treatment. Used for 48 weeks, 2x/day in 393 men, hair counts were 45% higher in men receiving 5% solution than 2%, and almost 5 times that of placebo. In another study, 96-week treatment showed increase in hair weight (frontal area sample) about 30% greater than placebo. Hair was rapidly lost after treatment was stopped.
One ml of minoxidil solution must be applied twice daily to achieve and maintain the effect. It is applied and spread lightly; does not need to be massaged in. The adverse effects are mainly dermatologic. Irritation of the scalp, dryness, scaling, itching, redness occurs in 7% of those who use the 2% solution and in more of those who use the 5% solution. Neither the 5% nor 2% solution alters blood pressure or pulse rate (serum levels 1.2ng/ml with 5% - 20.0 ng/ml needed for hemodynamic effect).
The 2% solution was approved for use in women in 1991. After 32 weeks (in 8 women), the average total hair weight increased by 42.5% compared to 1.9% in the placebo group. In another study, the 5% solution was no more effective. A one-year study is underway comparing the 2 solutions in 500 women. Hypertrichosis is more common in women, occurring above the eyebrows, in the malar region, laterally on the cheeks, and occasionally upper lip and chin. Hypertrichosis diminishes or disappears after 1 year.
Finasteride is a newer agent approved by the FDA in 1997 for stimulation of hair growth. It is a competitive inhibitor of type 2 5-alpha reductase and inhibits the conversion of testosterone to dihydrotestosterone. The rationale for its use is that men with this enzyme deficiency to not develop androgenetic alopecia. In 3 randomized, double blind, placebo-controlled studies, men received 1 mg/day orally for one year with a significant increase in hair counts and scalp coverage on photos. After 2 years, about 2/3 of men have improved scalp coverage, about 1/3 have the same amount of hair, and 1% lose hair. It may not be as effective in men over 60. The drug is well tolerated, though there was a slight decrease in libido and erectile function compared to control which decreased gradually during the treatment period. Its use is contraindicated in women who are or may become pregnant. Use in postmenopausal women showed equal hair loss compared to placebo.