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, including cancer.
They're the images that helped make erectile dysfunction drugs a $3 billion business, but now doctors say those little pills may also save lives.
"I did ask them what on earth they were talking about," said Brian Kumnick, cancer patient.
Kumnick is fighting throat cancer. He's had months of radiation and surgery.
"The radiation, it's barbaric. It's really barbaric, and I've lost my taste buds, for example. I can't taste anything. Water tastes like acid going down," said Kumnick.
He's part of a clinical trial to see if Cialis can cure head and neck cancers.
"It'd be really nice to just take a pill that has a pleasant side effect," he said.
In preliminary studies, doctors at Johns Hopkins say Cialis energized patients' immune systems, so their bodies could fight the cancer. Next they'll test to see if the drug can shrink tumors.
"When we looked at the blood of head and neck cancer patients," said Dr. Joseph Califano, professor at the Department of Otolaryngology -Head and Neck Surgery, John Hopkins Hospital. "We could get their immune response to rev up to near normal levels, whereas they were suppressed maybe 75 percent, sometimes even 80 percent."
From fighting cancer, to helping hearts and lungs.
"I was like, what? They said, 'Yeah, the Viagra is due right now,'" said Mike Cooper, father.
Genevieve suffers from pulmonary hypertension, which causes her to pass out.
"We just hear heart transplant, lung transplant. It was devastating. She's my little girl," said Sandra Hernandez, Genevieve's mom.
Instead, doctors prescribed Viagra in liquid form to open up her blood vessels.
"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," said Dr. James Swift, pediatric intensive care.
Other conditions being assessed for treatment with ED drugs include diabetes, multiple sclerosis, chronic pelvic pain, strokes and even memory loss.