What is Finasteride?
Finasteride (brand names Proscar and Propecia by Merck, among other generic names) is a synthetic 5-alpha-reductase inhibitor, an inhibitor of the enzyme that converts testosterone to dihydrotestosterone (DHT). Finasteride is approved for the treatment of benign prostatic hyperplasia (BPH) and male pattern baldness (MPB).
In a 5-year study of men with mild to moderate hair loss, 2 out of 3 of the men who took 1 mg of finasteride daily regrew some hair, as measured by hair counts. In contrast, all of the men in the study who were not taking finasteride lost hair. In the same study, based on photographs that were reviewed by an independent panel of dermatologists, 48% of those treated with finasteride experienced visible regrowth of hair, and a further 42% had no further loss. Average hair count in the treatment group remained above baseline, and showed an increasing difference from hair count in the placebo group, for all five years of the study.

Finasteride is effective only for as long as it is taken; the hair gained or maintained is lost within 6–12 months of ceasing therapy. In clinical studies, finasteride, like minoxidil, was shown to work on both the crown area and the hairline, but is most successful in the crown area.
Some users, in an effort to save money, buy Proscar (finasteride 5 mg) instead of Propecia, and split the Proscar pills into several parts to approximate the Propecia dosage. The pills are coated to prevent contact with the active ingredient during handling, and the dust or crumbs from broken Proscar tablets should be kept away from pregnant women or women who may become pregnant.

There have been case reports of persistent diminished libido or erectile dysfunction, even after stopping the drug. In December 2008, the Swedish Medical Products agency concluded a safety investigation of finasteride and subsequently advised that the use of finasteride may result in irreversible sexual dysfunction. The Agency’s updated safety information lists difficulty in obtaining an erection that persists indefinitely, even after the discontinuation of finasteride, as a possible side effect of the drug.

The UK’s Medical and Healthcare Products Regulatory Agency (MHRA) say that erectile dysfunction that persists once use of finasteride has stopped has been reported to them. Similar labeling changes have been made by the Italian government. For a period of time there was a discrepancy between European and North American warning labels regarding the risks of developing persistent sexual side effects from taking Propecia but after two years in April 2011 Merck revised the United States’ warning in consumer and medical leaflets to include erectile dysfunction that may persist after stopping finasteride. In April 2012, the FDA chose to approve Merck’s proposal from 2011 only after the warning label was further strengthened to include reports of libido disorders, ejaculation disorders, orgasm disorders, and decreased libido.

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