More than 30 million men take them for erectile dysfunction, but the drugs marketed to treat male impotence are now being investigated for the treatment of more than a dozen diseases and health problems. Researchers say ED drugs like Viagra could turn out to be as versatile as aspirin.

They're the images of happy couples that helped make erectile dysfunction drugs a $3 billion business. But now doctors say those little pills may also save lives.

Brian Kumnick is fighting throat cancer. He's been through months of radiation and surgery.

“The radiation, it's barbaric,” Kumnick told Ivnahoe. “It's really barbaric, and I've lost my taste buds, for example. I can't taste anything. Water tastes like acid going down."

He's part of a clinical trial to see if the ED drug Cialis can cure head and neck cancers.

"It'd be really nice to just take a pill that has a pleasant side effect,” Kumnick said.

In preliminary studies, doctors at Johns Hopkins say Cialis energized patients' immune systems so their bodies could battle the cancer cells. Next, they'll test to see if the drug also shrinks tumors.

"When we looked at the blood of head and neck cancer patients, we could get their immune response to rev up to near normal levels, whereas they were suppressed maybe 75 percent, sometimes even 80 percent,” Joseph Califano, M.D., professor in the Department of Otolaryngology-Head and Neck Surgery at Johns Hopkins Hospital in Baltimore, Md., told Ivanhoe.

From fighting cancer, to helping hearts and lungs ... doctors have found another use for Viagra.

Genevieve suffers from pulmonary hypertension -- lack of oxygen causes her to pass out.

"We just hear heart transplant, lung transplant,” Genevieve’s mother, Sandra Hernandez, told Ivanhoe. “It was devastating. She's my little girl."

Instead of a transplant, doctors prescribed Viagra in liquid form to open up Genevieve’s blood vessels.

“I was like, what? They said, ‘Yeah, the Viagra is due right now,’" father Mike Cooper said.

“Nitric oxide was developed for these types of issues in the lungs, and one of the byproducts was, hey, this medication also can dilate blood vessels in other parts of the body and treat erectile dysfunction,” James Swift, M.D., a pediatric intensive care physician at Sunrise Children’s Hospital in Las Vegas, Nev., told Ivanhoe.

They’re new possibilities for well-known drugs.

"It's very exciting to work with drugs that have already had safety data documented on them, because they can be very quickly moved into helping patients,” Dr. Califano said.

Other conditions being assessed for treatment with ED drugs include diabetes, multiple sclerosis, chronic pelvic pain, strokes and even memory loss. One study reports that Viagra increased blood flow and improved glucose processes in the brain, improving learning abilities.