The Grapevine

Finasteride's Sexual Dysfunction Side Effects Poorly Reported In Male Baldness Studies

finasteride
Finasteride has a swirling controversy behind it, and new research argues its risks aren't getting communicated. ryan, CC BY 2.0

Out of 34 clinical trials reviewed on the popular hair loss drug finasteride, zero were found to properly relay safety information on the drug’s controversial side effect of sexual dysfunction. Researchers from Northwestern University’s Feinberg School of Medicine report on the findings in a new meta-analysis published in JAMA Dermatology.

Finasteride is the active ingredient in two medications: Proscar, which was FDA-approved in 1992 for the treatment of enlarged prostate, and Propecia, which earned approval in 1997 as a treatment for androgenic alopecia (AGA), more commonly known as male pattern baldness. Since both drugs’ approval, however, rare yet well-popularized cases have emerged that question finasteride’s safety in regard to male fertility. A causal link has never been determined, but researchers remain wary.

“People who take or prescribe the drug assume it’s safe, but there is insufficient information to make that judgment,” said lead study author Dr. Steven Belknap, research assistant professor of dermatology at Northwestern.

Belknap and his colleagues recently took a hard look at the literature on finasteride, hoping to see how well recent trials highlighted the drug’s sexual dysfunction risks. Finasteride works by blocking an enzyme that lives in the scalp and sexual organs and converts testosterone into the more potent sex steroid dihydrotestosterone, or DHT. When that enzyme doesn’t convert, sexual function can get caught in the crossfire. According to the team’s review, however, these risks aren’t getting communicated.

“Our findings raise several questions,” Belknap said. “Why do the published reports of these 34 clinical trials not provide adequate information about the severity and frequency of sexual toxicity? Was this information obtained but then not included in published articles?” While malice may explain why the evidence was omitted, Belknap suspects a more likely reading is that the researchers behind the 34 trials weren’t able to include it because their tests simply didn’t produce that data.

For patients, the evidence that does exist is mixed. In 2010, the FDA began requiring Merck, the manufacturer of Proscar and Propecia, to include on their labels a warning regarding finasteride’s possible effects on erectile dysfunction, semen quality, and other sexual disorders that may persist after discontinuing the drug. This was due to hundreds of reports the agency received over multiple years that both drugs were causing problems. However, despite no causal link, the FDA still states that “prescribers and patients need to be aware” of these adverse events.

Chief among the dangers is the side effects’ duration, although the data would suggest the risks are low over the long-term. A 2002 study, for instance, found drug-related sexual side effects occurred in less than two percent of men. Another study, conducted in 2007 with more than 18,000 men, discovered sexual dysfunction increased “only slightly” and its impact “diminished over time.”

Belknap and his team’s discovery leaves some questions to be answered. Finasteride has been well-established as a method for prostate cancer prevention through a reduction in the prostate’s size. But the collateral damage of reduced sexual function is still highly elusive, and a lack of transparency only contributes to the fear of the unknown.

“One might reasonably expect that 34 studies and two meta–analyses would be adequate to establish the rate of finasteride adverse effects in AGA,” the researchers concluded, “yet this does not appear to be the case.”

Source: Belknap S, Aslam I, Kiguradze T, et al. Adverse Event Reporting in Clinical Trials of Finasteride for Androgenic Alopecia. JAMA Dermatology. 2015.

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