Propecia (Finasteride)
Male pattern baldness or androgenetic alopecia is caused by the effects of the male hormone dihydrotestosterone (DHT) on genetically susceptible hair follicles that are present mainly in the front, top, and crown of the scalp (rather than the back and sides). DHT causes hair loss by shortening the growth, or anagen, phase of the hair cycle, causing miniaturization (decreased size) of the follicles. The effected hair becomes progressively shorter and finer until it eventually disappears. (See Cause of Hair Loss in Men)

DHT is formed by the action of the enzyme 5-alpha reductase on testosterone. Finasteride is a drug that works by blocking the enzyme 5-alpha reductase Type II that converts testosterone to dihydrotestosterone (DHT) in the hair follicle. Propecia, the brand name for finasteride, is the only FDA approved oral medication for hair loss.
Finasteride causes a significant drop in both scalp and blood levels of DHT and its effect is felt to be related to both of these factors. Finasteride 1-mg/day decreases serum DHT levels by almost 70%. Serum testosterone levels actually increased by 9%, but this is within the range of normal.

It is commonly thought that finasteride was first conceived as a prostate medication and that, only by chance, was found to prevent hair loss. The fact is that in 1974 the researcher Imperato-McGinley described a group of genetically male children from the village of Salinas in the Dominican Republic who were deficient in the enzyme 5-alpha reductase. These male children had very low levels of DHT and throughout their life, their prostates remained small and they did not develop male pattern hair loss or acne.

The objective of the researchers was to find a drug that could block the 5-alpha reductase enzyme and mimic the abnormality found in these men. They could then use this drug to prevent both prostate enlargement (BPH) and hair loss. The decision was made, however, to obtain FDA approval for the medical indication first, rather than the cosmetic one. As a result, in 1992, Finasteride 5-mg was released under the brand name Proscar, for use in men over 50 with prostate enlargement (the prostate also has the type II enzyme). Five years later, i n 1997, the FDA approved finasteride 1-mg/day (Propecia) for the treatment of male pattern baldness.
Side Effects
Side effects from finasteride at the 1-mg dose are uncommon, but reversible. The one- year drug related side effects were 1.5% greater than in the control group. The data showed that 3.8% of men taking finasteride 1mg experienced some form of sexual dysfunction verses 2.1% in men treated with a placebo. The five-year side effects profile included: decreased libido (0.3%), erectile dysfunction (0.3%), and decreased volume of ejaculate (0.0%).

Most reported cases of sexual dysfunction occurred soon after starting the medication, but there have been reports of sexual dysfunction that have occurred at later points in time. The sexual side effects were reversed in all men who discontinued therapy, and in 58% of those who continued treatment. After the medication was stopped, side effects generally disappeared within a few weeks. When finasteride is discontinued, only the hair that had been gained or preserved by the medication is lost. In effect, the patient returns to the level of balding where he would have been had he never used the drug in the first place. No drug interactions of clinical importance have been identified.
Generic Finasteride
Finasteride 5mg (Proscar) is available in a generic formulation. (Propecia) will not be available generically until the year 2012. For those wanting to take generic finasteride, we recommend buying a pill cutter at the pharmacy and taking � of a 5mg tablet every day. Please be advised that there is no scientific data insuring that this will be as effective as Propecia 1mg a day. Also, remember that there is a potential risk to pregnant women from handling broken or crushed tablets (see Caution during Pregnancy).
Patient Monitoring
It is recommended that men aged 50, or over, should inform their regular physicians or urologists that they are taking Propecia (finasteride 1mg). It is also recommended that all men aged 50 or over have a routine annual evaluation for prostate disease, regardless of whether or not Propecia is used. For those patients who are black and/or who have a family history of prostate disease, these recommendations would apply beginning at age 40. An evaluation may include a rectal examination, a baseline PSA, and other tests that your examining physician feels are appropriate.