Propecia was approved by the U.S. Food and Drug Administration in 1997, and at that time Merck noted that a few men reported sexual side effects during clinical trials of the drug. On its website, the agency said those side effects were resolved when patients stopped taking the drug.
But the agency received more than 400 reports over 13 years from consumers reporting sexual dysfunction, and nearly 60 men reported that those side effects lasted longer than three months after the men stopped the medication. In 2011, the FDA mandated a label change for Propecia and Proscar, warning that some patients reported erectile dysfunction that lasted after patients stopped taking it; in April, the agency updated the label to include reports of libido, ejaculation and orgasm disorders.
In a statement, Merck said no evidence has proved a causal relationship between Propecia and long-lasting sexual dysfunction.
"Merck believes that Propecia (finasteride) has demonstrated safety and efficacy profiles and that the product labeling appropriately describes the benefits and risks of the drug to help inform prescribing," the company wrote in the statement.
But researchers say many physicians who prescribe finasteride are likely not aware that the side effects of the drug may haunt patients for years.
"These things just get handed out left and right for any urinary symptoms," said Dr. Ryan Terlecki, an assistant professor of urology at Wake Forest School of Medicine, who has prescribed Proscar for some of his patients with enlarged prostates.
Terlecki said the findings about long-term side effects from the drug are alarming, but more research will likely be needed before doctors can know for sure that the symptoms are completely attributed to the drug.
"There are so many things that go into the male erectile response," he said. "You have to be very careful before you attribute it to one cause or another."
Men Report Neurological Side Effects, Too
Malley said before he took Propecia, he was a normal, ambitious guy. He was engaged and worked as a public health researcher at a university in Las Vegas.
"Before, I would get up at eight in the morning, go to work, go to school, go to the gym, come home, have sex with my girlfriend. I had a lot of ambition, I had career goals," he said. "Now basically I just sit in my room all day and don't talk to anyone."
His fiancée broke off their engagement, and Malley had to resign from his job because of his persistent cognitive symptoms. He has sought treatment for these side effects, but doctors told him there's nothing they can do for him. He said he is angry that no one told him that the drug might change his life so dramatically.
"Even if the side effects are rare, that doesn't mean that I should not have been warned. I did have a life before this," he said.
Steven Rossello, 29, said his doctor made no mention of the potential for any sort of side effects from finasteride when he prescribed it to treat Rossello's hair loss in 2010.
"That's what really makes me really mad. He never mentioned any side effects, not to mention that they last forever," Rossello said.
But after four months of taking Propecia, Rossello said he began suffering anxiety and crippling depression, along with the drug's sexual side effects, and decided to stop taking the drug.