Kevin Malley was almost 30, and he was starting to lose his hair. He went to his doctor to see if there was a way to keep from going bald, and his doctor prescribed Propecia.

"I looked young for my age, so I wanted to hold off my hair loss for a little bit," Malley said. "I didn't plan on taking Propecia for more than a year."

Malley started taking the drug in May 2011, and by October he was completely impotent and had no sex drive whatsoever. His body changed, even his genitals shrank, and he slipped into a mental fog that he just couldn't clear. His doctor told him the side effects would go away if he stopped taking the drug, so he did. But nothing changed.

"I kept expecting the side effects to go away, but they did not, they only got worse," he said.

Malley is not alone: A new study published today in the Journal of Sexual Medicine suggests that for some men, the sexual side effects of Propecia may last for months to years, even after they stop taking the drug.

Researchers from George Washington University interviewed 54 men under age 40 who reported side effects for three months or more after taking Propecia, also called finasteride, to treat their hair loss. None of the men reported having any sexual, medical or psychiatric problems before they took the drug. Some of the men took the drug for a few weeks, others took it for years, but all of them reported side effects such as erectile dysfunction, decreased sexual drive, problems with orgasms, shrinking and painful genitals, even some neurological problems, such as depression, anxiety and mental fogginess.

For 96 percent of the men, the sexual problems lasted for more than a year after they stopped taking the drug.

"Our findings make me suspicious that this drug may have done permanent damage to these men," said Dr. Michael Irwig, the author of the study. "The chances that they will improve? I think it's lower and lower the longer they have these side effects."

Irwig cautions that it's possible that only men who were the most affected by the drug participated in the study. Because he recruited his study participants through an online forum called PropeciaHelp, a group for men who have experienced persistent sexual side effects from the drug, he said the study may not have included men who have fewer or less pervasive side effects.

FDA, Merck Know of Drug's Side Effects

Finasteride works by blocking the conversion of testosterone into a more potent form, called DHT, which contributes to hair loss. It was originally developed in 1992 by drug giant Merck as a treatment for enlarged prostates and sold as the drug Proscar.

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.

But his symptoms only got worse. He was demoted from his job as an investigator for the Department of Homeland Security in Texas after his symptoms were evaluated by a psychiatrist, who pronounced him unfit for duty. Rossello said the psychiatrist was unfamiliar with the neurological side effects of Propecia.

Abdulmaged Traish, a professor of biochemistry and urology at Boston University School of Medicine, said scientists are just beginning to investigate finasteride's effects on the brain and nervous system.

"We are just beginning to venture in that direction. It might be in the next five to 10 years that we may find there's more to this story than we know now," Traish said.

He said he would not advise men to take this drug to treat a cosmetic problem like hair loss.

"Why take that chance? Telling the risks of the drug is fine, but most physicians don't sit and take the time to explain to their patients the possible effects of these drugs."

On its website, the FDA said only 36 of 945 men who took Propecia in clinical trials reported any adverse sexual side effects. Irwig agrees that the number of men who will experience these long-lasting side effects is relatively small, likely around 3 percent of all men who take the drug.

"But because the medication is prescribed so commonly, it's still a lot of people, likely several thousand men around the world," he said.

And currently, doctors have no way of knowing which patients will suffer the long-term side effects. Irvig said it's possible that an unknown genetic factor drives how individual men respond to the drug.

Both Malley and Rosello were not involved in Irwig's study, but they are two of many men who have joined class-action lawsuits against Merck over the side effects of Propecia. In May, Malley camped out in front of Merck's headquarters in New Jersey for a week, staging a hunger strike to protest the company's response to Propecia's side effects. A representative came out to deliver a letter to him, detailing how he could report his symptoms to the company.

Malley has a simple message for men who might consider taking Propecia for their hair loss.

"Stay away from it at all costs," he said.