Finasteride as Proscar® was originally used for the treatment of benign prostatic hypertrophy. Its mechanism of action is to bind to 5-alpha reductase, the enzyme that converts testosterone into its active form di-hidrotestosterone (DHT) that can cause prostate enlargement, acne, and hair loss. Taken orally, finasteride suppresses DHT formation with no change in testosterone, cortisol, prolactin or estradiol levels. Possible side effects include gynecomastia, erectile dysfunction, decreased libido, depression, and reduced quantity of ejaculate. These side effects occur with a low frequency, and are reversible upon stopping the drug.
Finasteride is most effective in the crown and back of the head, but also has some efficacy in the frontal half of the scalp, where it stabilizes hair loss and can increase hair density. While both men and women can potentially benefit from finasteride, it is only approved for use in men due to its risk in pregnant women where it can inhibit normal sexual development of the male fetus. Post-menopausal women are thus able to safely take the medication, however it is our personal experience that finasteride is not as effective in women as men.
The typical dose is 1mg daily, but there is some support in the medical literature for the use of 2.5 to 5mg doses. There is also a topical formulation of finasteride 0.1% that can be combined with minoxidil, but the efficacy is not known.
Dutasteride (Avodart®) is like finasteride, except it inhibits both types of the 5-alpha reductase enzymes, thus theoretically more effectively blocking the conversion of testosterone to DHT (dihydrotestosterone). However, dutasteride has not received FDA approval in the USA, and thus can only be used off-label for the treatment of androgenetic alopecia. Clinical trials have shown that dutasteride decreases the levels of serum DHT by 90% versus 70% with finasteride, and showed higher increases in hair counts, but it showed side effects such as a long-term reduction in sperm counts. Larger controlled studies are needed.