Before Propecia gained U.S. approval in 1997, manufacturer Merck & Co. released clinical trial data on the drug’s safety. One study revealed that nearly 4 percent of men treated with Propecia reported one or more adverse sexual side effects, compared with about 2 percent of men given a placebo.
The most commonly reported sexual side effects of Propecia include:
- Erectile dysfunction
- Ejaculation disorder
- Decreased libido
Although both Merck and the U.S. Food and Drug Administration (FDA) assured men 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 show Propecia’s sexual side effects can persist even after a man stops taking the drug. In some cases, the complications are irreversible.
One case study, for example, describes a 24-year-old man 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 considered rare, they can have a huge impact on quality of life for those affected. Men who claim they suffer persistent sexual dysfunction from Propecia use have filed about 1,370 lawsuits against Merck.
Erectile dysfunction is a side effect that repeatedly appears in Propecia studies, including double-blind, randomized and placebo-controlled trials. Drawing on data from six Propecia clinical trials, one review of the drug’s adverse sexual side effects reported that about 6 to 8 percent of patients experienced erectile dysfunction.
Erectile dysfunction is when a man has trouble getting or keeping an erection. It becomes more common as men get older, though it is not considered a natural part of aging.
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. Multiple 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 a 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 discontinuation, 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.
Propecia use also has been associated with several ejaculatory disorders. Ejaculatory disorders range from premature (rapid) ejaculation to delayed ejaculation to a complete inability to ejaculate.
Four percent of men taking finasteride experienced some ejaculatory disorder, compared with 1 percent of men taking a placebo, according to an AUA review. In addition, scientists have observed evidence of ejaculatory dysfunction in 20 finasteride trials.
Ejaculatory disorders associated with Propecia use include:
- Retrograde ejaculation (when semen goes backwards into the bladder rather than forwards out of the penis)
- Ejaculation failure
- Decrease in semen volume
Propecia Sexual Side Effects Studies
Five years before Propecia became available in the U.S., researchers linked doses of finasteride, Propecia’s main ingredient, to sexual side effects. According to a 1992 report in the New England Journal of Medicine, researchers found a higher incidence of impotence, ejaculatory disorders and decreased libido in finasteride users when compared with men who took a placebo.
Studies of the potential sexual side effects of finasteride continued in the years that followed the 1992 report; however, the findings were not given much public attention because those using the drug were mostly older men with enlarged prostates, making them more prone to underlying sexual dysfunction.
Concern for potential sexual side effects grew when young men began taking Propecia to treat hair loss.
But when the FDA approved Propecia for hair-loss treatment, younger men began taking finasteride and concern of potential sexual side effects grew. This is because younger men were “much less likely than older men with enlarged prostates to already have underlying sexual dysfunction,” according to a Washington Post report.
In 1998 — about one year after Propecia hit the market — more than 1,500 men between the ages of 18 and 41 participated in two yearlong trials in which they received either Propecia or a placebo. Researchers discovered 4.2 percent of men treated with Propecia reported sexual dysfunction, compared with 2.2 percent of men given a placebo.
“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,” Daniel Marchalik, a urologist at the MedStar Washington Hospital Center in D.C., wrote in the Washington Post report.
Persistent Sexual Side Effects
A 2003 study funded by Merck gave one of the earliest indications that the sexual side effects of finasteride may continue even after men stop using the drug. In the first year of treatment, 15 percent of men taking finasteride for an enlarged prostate reported sexual side effects. Researchers said side effects later resolved in 50 percent of men, and the group with persistent sexual complications received no follow-up.
The 2003 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 problems with erectile function, arousal, sexual desire, orgasm and orgasm satisfaction. These side effects appeared slowly and persisted for an average of 40 months after the end of treatment.
Side effects that appeared as a result of taking finasteride 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.
More recently in March 2017, a Northwestern Medicine study found that men who take finasteride can get persistent erectile dysfunction in which they will not be able to have normal erections for months or years after stopping finasteride. The study evaluated data from 11,909 men for persistent erectile dysfunction. Eligible men were 16 to 89 years old and had at least one clinical encounter and one diagnosis from January 1992 to September 2013.
Of the men studied, 1.4 percent developed persistent erectile dysfunction that continued for an average of about 1,350 days after stopping treatment. Men 41 years old and younger who had more than 205 days of exposure to finasteride or to the related drug dutasteride had nearly five times higher risk of persistent erectile dysfunction than men with shorter exposure.
FDA Strengthens Propecia Side Effect Warnings
Between 1998 and 2011, the FDA received more than 420 reports of sexual dysfunction in Propecia users. Nearly 60 men reported side effects that lasted longer than three months after they stopped using the drug, including erectile dysfunction, decreased libido, problems with ejaculation and orgasm disorders. More than 250 cases involved semen quality associated with Propecia.
In 2011, the FDA required the drug’s label include information about incidences of male breast cancer, an increased risk of high-grade prostate cancer and the potential of erectile dysfunction after stopping use of the drug.
Then in April 2012, the FDA required revisions to the Propecia label to include libido disorders, ejaculation disorders and orgasm disorders that continued after discontinuation of the drug, as well as a description of reports of male infertility and/or poor semen quality that normalized or improved after drug discontinuation.
Emily Miller holds five Health Literacy certificates from the Centers for Disease Control and Prevention as well as a Bachelor of Science in Journalism from the University of Florida. She is a member of The Alliance of Professional Health Advocates and the American Association for the Advancement of Science. Emily was diagnosed with a chronic illness as a child and has firsthand experience with many of the topics she writes about as a member of the Drugwatch team. She is an award-winning journalist who has reported on health and legal news for reputable organizations, including the South Florida Sun Sentinel, San Antonio Express-News, UF Health News and Reporters Committee for Freedom of the Press. She draws on her background as both a patient and a journalist to help readers understand complex health and legal topics.