In a 5-year study of men with mild to moderate hair loss, 48% of those treated with Propecia (finasteride 1mg) experienced some regrowth of hair, and 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. Propecia 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, Propecia, 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 instead of Propecia, and split the Proscar pills to approximate the Propecia dosage. Doing so is generally considered unadvisable if women of pregnancy age are in the household; this is because finasteride, even in small concentrations, can cause birth defects in a developing male fetus. The birth defects involve the development of male genitalia (no such effects have been noted in developing female fetuses). On most product inserts, it will be mentioned that the dust or crumbs from broken Propecia tablets should be kept away from pregnant women.

Propecia has been shown to be ineffective for treating hair loss in women.[citation needed] However, Propecia's supporters respond that the study was on post-menopausal women whose hair loss was more likely related to the loss of estrogen versus a sensitivity to testosterone. Many doctors prescribe it for women, but not without either careful birth control measures or assurance that the woman cannot become pregnant.

Possible health concerns

The UC Berkeley Wellness Letter expressed concern in March 2003 about the unproven long-term safety of Propecia and recommended cutting a standard 1 milligram dose of Propecia into quarters to reduce the cost without reducing its effectiveness. This claim appears to be supported by clinical pharmacological data reviewed by the FDA during Propecia's approval process that suggested that the advantage of taking 1 mg per day over 0.2 mg per day is statisticially small. Some people have unsuccessfully petitioned the FDA to re-examine the approved dosage in light of the statistical evidence and unknown long-term risks. The FDA responded and said that just because the level of DHT found in the scalp was not significantly different does not mean there is a correlation with hair loss. A study would have to show that the benefits of using 0.2 mg and 1 mg were not statistically different. According to the FDA such a study has been performed and a 1 mg dose has a greater benefit whilst remaining equally safe. The same study also concluded that doses of 0.01 mg per day were found to be ineffective in treating hair loss.

In the Prostate Cancer Prevention Trial (PCPT), 25 percent fewer men taking the drug finasteride developed prostate cancer than men not taking the drug. However, men who developed prostate cancer while taking finasteride were more likely to have high-grade cancers, which can spread quickly even if the tumors are small.

Propecia's effects in detail

DHT is a derivative hormone (metabolite) of testosterone that has been shown to be critical to the initiation and progression of follicular miniaturization and eventual destruction of hair follicles in male pattern baldness. DHT is a steroid hormone just like testosterone but with greater affinity for the androgen receptor. Converting testosterone to DHT thus increases many of its effects.

While the mechanism by which DHT is involved in hair loss is not confirmed, many dermatologists and research scientists specializing in hair loss believe DHT molecules may diffuse into the interior of hair follicle cells (the cytoplasm or cytosol) and bind with androgen receptors. This complex, both the receptor and the DHT molecule, then enters the nucleus of the cell. In the nucleus of the hair follicle cell this complex could then alter the rate of protein synthesis in men who are genetically predisposed to baldness.

However, DHT also plays an important role in the functioning of the central nervous system (the brain), the testicles and prostate, and almost everything but muscle tissue. In muscle tissue testosterone is the dominant hormone, which is why some bodybuilders inject testosterone derivatives to aid in muscular development.

* Propecia (and other products containing finasteride) cause a rise in testosterone levels because testosterone that would normally be converted into DHT remains testosterone. Continual high levels of testosterone in the body could possibly have negative side effects.

* Artificially low levels of DHT in the body could cause some unwanted conditions. DHT is an antagonist of estrogen. Men’s bodies also produce the female hormone estrogen in the adrenal glands, although this is just one-tenth of the estrogen that premenopausal women produce in their ovaries. By reducing DHT with drugs, a man’s protection from the effects of estrogen may also be reduced. This could result in gynecomastia.

* Even though both finasteride and dutasteride were developed to combat benign prostatic hyperplasia by reducing DHT in prostate tissue, some scientists question the wisdom of using these 5-alpha reductase inhibitors in younger men who have no problem with their prostates. A research chemist, Patrick Arnold, says “Evidence is mounting that the existence of a high estrogen/androgen ratio – a condition common in older men – is highly correlated with the development of benign prostatic hyperplasia.” However, in apparent contradiction, individuals with 5-alpha-reductase deficiency (and thus a similar hormonal profile to users of DHT inhibitors) do not experience BPH.