It's called off-label drug use, when drugs meant for a specific condition are prescribed to treat another ailment.

Doctors around the country are doing it for patients whose other treatments have failed. There are plenty of benefits, but some potential dangers too.

To hear Marquita Lister now, you'd never know she almost lost it all.

Marquita Lister is an opera singer and explained how good her life has been by saying, "I've had the kind of life that people only dream about."

The international opera star was diagnosed with Polymyositis. It attacks the lungs and muscles.

"I almost died," Lister said.

A medical team at National Rehabilitation Hospital came up with an innovative form of therapy, including a drug normally used to treat lymphoma patients.

Doctors took a chance with the off-label drug use, and it paid off. Marquita pulled through.

Experts say, as many as one in five prescriptions in the US is used for something it's not approved for by the FDA. And it's perfectly legal.

Antipsychotic drugs are often prescribed for dementia, anxiety drugs are used as sleep aids, and some cancer drugs for eye problems.

Off-label drugs worked for Marquita, but they aren't safe in all cases. Studies show some anti-psychotics used to treat elderly patients with dementia did show benefits, but also increased risk of death.

Other studies found a drug used to help patients from bleeding uncontrollably during surgery. Increased the odds of blood clots, when used off-label.

While studies and results may differ on the practice, off-label drugs got Marquita back on stage. For her the risk was worth it.

Meanwhile, off-label drug use is possible, because once the FDA approves drugs, physicians are allowed to use their own judgment on what they're prescribed for.

However, the FDA bars drug makers from promoting their products for off-label use. There's a legal battle brewing over that right now.

Manufacturers are fighting the off-label rule in court, claiming the ban violates their first amendment rights.