Merck sells finasteride under the brand name Propecia, a 1-milligram formulation of the medication. It is available as a prescription for treatment of male-pattern hair loss. Its big brother, Proscar, is a 5 mg preparation commonly prescribed for the treatment of symptoms associated with enlarged prostate, or benign prostatic hyperplasia, and has been prescribed to more than 1 million American men since its introduction to the market. Together, finasteride and a closely related compound dutasteride (sold under the brand name Avodart) are a class of drugs called 5-alpha-reductase-inhibitors (5-ARIs) which work by blocking the conversion of testosterone to its more potent form, dihydrotestosterone.

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Between Propecia, Proscar and Avodart, 5-ARIs comprise a substantial portion of medications prescribed to men every year. As a urologist, I prescribe or see men who have been prescribed these medications quite often. After all, the drugs have a variety of important uses in older men with enlarged prostates. But in speaking to my patients, I have come to realize how often men are not aware of the potentially life-changing and irreversible side effects that may be associated with these medications.

The constellation of potential symptoms, sometimes referred to as post-finasteride syndrome, may include sexual, physical and psychological changes. Of these, the sexual side effects are perhaps the most extensively reported. In fact, in 2012, the Food and Drug Administration announced a label change for Propecia and Proscar, requiring the manufacturer to warn that the medication may be associated with “libido disorders, ejaculation disorders, and orgasm disorders that continued after discontinuation of the drug.”

The systematic study of the side effects of finasteride can be traced back to a report in the New England Journal of Medicine in 1992 — the year Proscar was initially approved by the FDA for its use in benign prostatic hyperplasia. Studying both the 1 mg and 5 mg doses of finasteride, the researchers demonstrated a higher incidence of impotence, ejaculatory disorders and decreased libido in both treatment groups when compared with a placebo. Although these complications were consistently studied over subsequent years, the conversation remained far from the public sphere, in part because of the older age of patients taking Proscar for enlarged prostate.

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Then, in 1997, the FDA’s approval of Propecia for use in hair loss created a sudden increase in finasteride prescriptions in a new group of patients — younger men. With it came a heightened concern of potential sexual side effects, because this cohort was much less likely than older men with enlarged prostates to already have underlying sexual dysfunction.

In 1998, two year-long trials were conducted with more than 1,500 men ages 18 to 41 receiving either Propecia or a placebo. The rate of sexual dysfunction in the finasteride group was about double that of the placebo group (4.2 percent compared with 2.2 percent). Because this trial was designed to study the hair-restoring qualities of finasteride, and the assessment of sexual side effects does not appear to have been rigorously conducted, the extent of the side effects may very well have been underreported.

An even larger concern surfaced when reports arose of men having persistent side effects even after the medication was discontinued. A 2012 study in the Journal of Sexual Medicine attempted to determine whether the symptoms really could be long-lasting or irreversible. Fifty-four men under 40 who had continued sexual dysfunction despite a three-month cessation of finasteride therapy were reassessed at an average of 14 months. Ninety-six percent of these men continued to have persistent sexual dysfunction despite no further treatment with finasteride.

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Earlier this year, a review of 17 randomized controlled trials (including more than 17,000 patients) demonstrated a nearly twofold increase in sexual, ejaculatory and orgasmic dysfunction in young men using Propecia for male pattern hair loss.

At the same time, a recent study demonstrated changes in the levels of certain steroids in cerebrospinal fluid of men taking finasteride for hair loss. These steroids have been shown to influence brain function, and their presence may help explain the profound psychological changes such as depression and suicidality that have been associated with finasteride use.

This research should cause us to think more carefully about this commonly encountered medication. It is perhaps most worrisome because Propecia tends to target younger men, who have a relatively low rate of sexual dysfunction. And the ease with which it is prescribed for purely cosmetic reasons makes the potential risk of side effects even harder to justify.

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For those of us in urology, finasteride will inevitably remain an important treatment tool for certain medical conditions. But because recent data suggests that finasteride-associated side effects may persist even after the medication is stopped, the key intervention must consist of both adequately counseling patients on the potential harms of these drugs and of carefully selecting the patients who are best candidates for receiving this medication in the first place.

Whether this medication is safe for individuals holding political office has not been studied.

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