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Propecia Side Effects: Erectile Dysfunction & Decreased Libido


The hair loss drug Propecia can cause sexual side effects. In some cases, these complications do not go away.

After just one year on the market, more than 400,000 men in the United States were filling prescriptions for Propecia to reverse their male pattern baldness. While the drug’s active ingredient, finasteride, effectively blocks the hormone responsible for this common genetic form of hair loss, numerous studies suggest that it can also have damaging effects on users’ sexual health.

Before Propecia was approved for use in the United States in 1997, manufacturer Merck & Co. released clinical trial data on the drug’s safety. One study revealed that 3.8 percent of men treated with Propecia reported one or more adverse sexual side effects, compared with 2 percent of those given a placebo.

The most commonly reported sexual side effects of Propecia include:

  • Erectile dysfunction
  • Ejaculation disorder
  • Decreased libido

While both Merck and the Food and Drug Administration (FDA) assured patients that these complications would resolve once they stopped taking Propecia, later evidence would prove the contrary.

The preapproval trials were not especially reliable, as the information was drawn from a relatively small patient group treated for only six months to one year, and follow-up procedures were unclear. More recent investigations demonstrate that Propecia’s sexual side effects can persist even after cessation of use. In some cases, the complications are irreversible.

One case study describes a 24-year-old patient who started taking Propecia in 1999. Within one week, he experienced soreness in his testicles, a lack of sex drive and the inability to achieve an erection. He stopped taking the drug about a month later, and while some side effects disappeared, his sexual function never returned to normal. In a follow-up 11 years later, he still suffered from erectile dysfunction and loss of libido.

Although situations like this are rare, they can have a huge impact on quality of life for those affected. Starting in April 2012, claimants suffering persistent sexual dysfunction from Propecia use began filing lawsuits against Merck & Co. To better manage the growing caseload, the Propecia lawsuits were consolidated into a multidistrict litigation: MDL 2331. By January 2013, the MDL had grown to 139 lawsuits. More than 250 additional claims have been filed in New Jersey state courts.

Persistent Sexual Side Effects

One of the earliest indications that the sexual side effects of finasteride may continue even after patients stop using the drug came from a 2003 study funded by Merck. In the first year of treatment, 15 percent of men taking finasteride for an enlarged prostate (the drug’s other approved use) reported sexual side effects. Researchers stated that side effects later resolved in 50 percent of patients, but the other group with persistent sexual complications received no follow-up. The study concluded that the problems were most likely caused by factors unrelated to the drug.

This claim was challenged in 2011, when George Washington University urologist Michael S. Irwig and his colleague Swapna Kolukula published an assessment of 71 finasteride patients who reported long-term sexual side effects that persisted after discontinuation of the drug.

The selected group of patients, young men between the ages of 21 and 46, took a survey that revealed a wide range of sexual side effects that arose after Propecia use, including issues with erectile function, arousal, sexual desire, orgasm and orgasm satisfaction. These side effects appeared slowly and gradually, and persisted for an average of 40 months after the end of treatment.

Upon following up with 51 of these patients one year later, Irwig discovered that 96 percent of the men were still suffering from the sexual dysfunctions they initially reported. None of the men reported sexual, psychiatric or medical complaints before taking finasteride.

By 2012, the FDA published results from its own investigation into the adverse effects of finasteride. Using data collected from 1998 to 2011, this study identified persistent sexual dysfunction of at least three months in 14 percent of the 421 evaluated cases. While the agency stated that a clear causal link between finasteride and sexual side effects had not been established, warnings of these complications were added to the drug’s prescribing information.

Erectile Dysfunction

Drawing on data from six Propecia clinical trials, one review of the drug’s adverse sexual side effects reported that approximately 6 to 8 percent of patients experienced erectile dysfunction. This side effect repeatedly appears in Propecia studies, including double-blind, randomized and placebo-controlled trials.

Symptoms of erectile dysfunction may be persistent, and include:

  • Difficulty getting an erection
  • Difficulty maintaining an erection
  • Low sexual desire

In a large observational cohort study of 14,772 men taking finasteride, erectile dysfunction was the most frequently reported of all side effects; 143 patients (roughly 1 percent of those involved) withdrew from treatment as a direct result of erectile dysfunction. According to the American Urological Association (AUA), erectile problems affected 8 percent of men on finasteride and 4 percent of those taking a placebo.

These complications can likely be attributed to Propecia’s suppression of DHT, a hormone that plays an important role in erectile physiology. Numerous animal and human studies have confirmed that Propecia and other 5-alpha-reductase inhibitor drugs can have an adverse effect on erectile response.

While lowering the body’s levels of DHT may correct hair loss, problems arise because this sex hormone is important for maintaining the structural integrity of nerves, smooth muscle, connective tissue and signaling pathways in the penis.

Loss of Libido

Another Propecia side effect that may persist long after men stop taking the drug is a reduced interest in sex. The AUA clinical practice guideline states that 5 percent of men taking finasteride experience a loss of libido, compared with 3 percent of the men given a placebo.

In Irwig and Kolukula’s study of 71 patients who experienced Propecia sexual side effects, 94 percent of men experienced  a decline in libido. The average duration of all sexual side effects, measured from the time of drug cessation, was 40 months.

While a persistent reduction in libido only occurs in a small subset of patients, it can be devastating for those affected. The problem can threaten relationships and often has a severe emotional toll on men and their partners.

Ejaculatory Disorder

Evidence of ejaculatory dysfunction has been observed in 20 finasteride trials, as well as in trials for other 5-alpha-reductase inhibitors like dutasteride. In one study, finasteride and dutasteride led to a decrease in ejaculatory function in week 26 and week 52 of treatment, according to results of a sexual function inventory.

Propecia use has been associated with numerous ejaculatory disorders, including retrograde ejaculation, ejaculation failure and a decrease in semen volume. According to the AUA clinical practice guideline’s review of 5-alpha-reductase inhibitor trials, 4 percent of men taking finasteride experienced some ejaculatory disorder, compared with 1 percent of men taking a placebo.