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(CBS/AP) Medicines generally have side effects, but once in awhile the side effects may treat other conditions. Viagra after all, was originally a blood pressure medicine. Amantadine, an old flu medicine approved in the 1960s, was found a few years later to improve symptoms of Parkinson’s disease. now a new study shows the drug may also speed recovery from severe brain injuries.

The study, published Mar. 1 in the New England Journal of Medicine, involved 184 patients who had severe brain injuries caused by falls and car crashes. about a third were in a vegetative state (unconscious but with periods of wakefulness) and the rest were minimally conscious.

The patients were randomly assigned to receive amantadine or a placebo daily for four weeks. They were treated within one to four months after getting injuried – a period when a lot of patients get better on their own, according to study author Joseph Giacino, a neurologist at Boston’s Spaulding Rehabilitation Hospital.

The researchers found both groups made small but significant improvements, but the rate of recovery was faster in the group getting amantadine. changes included the ability to give yes-and-no answers, follow commands or use a spoon or hairbrush. Of the patients who received amantadine, only 17 percent remained in a vegetative state, versus 32 percent of those who received the dummy drug.

When treatment stopped, recovery in the amantadine group slowed and two weeks later, the level of recovery in the two groups was about the same.

The study was short, and the effect on long-term outcome is unknown. But Giacino said the drug still has value even if it only hastens recovery. The study also didn’t include those with penetrating head injuries, like the gunshot wound former Rep. Gabrielle Giffords suffered, but Giacino said the drug should have similar effects in those patients. whether it would work in patients with brain injuries not caused by trauma, such as a stroke, isn’t known.

“This drug moved the needle in terms of speeding patient recovery, and that’s not been shown before,” Giacino said. “It really does provide hope for a population that is viewed in many places as hopeless.”

Many doctors began using amantadine for brain injuries years ago, but until now there’s never been a big study to show that it works.

Doctors first had an inkling that the inexpensive generic amantadine might have other uses a few years after its approval when it appeared to improve Parkinson’s symptoms in nursing home patients. it was found to have an effect on the brain’s dopamine system, whose many functions include movement and alertness, and it was eventually approved for Parkinson’s.

It’s now commonly used for brain injuries, and the researchers felt it was important to find out “whether we’re treating patients with a useful drug, a harmful drug or a useless drug,” said study author Dr. John Whyte, director of the Moss Rehabilitation Research Institute in suburban Philadelphia.

Each year, an estimated 1.7 million Americans suffer a traumatic brain injury. Falls, car crashes, colliding with or getting hit by an object, and assaults are the leading causes. about three-quarters are concussions or other mild forms that heal over time. But about 52,000 people with brain injuries die each year and 275,000 are hospitalized, many with persistent, debilitating injuries, according to government figures.

The study didn’t include those with penetrating head injuries, such as gunshot wounds, but Giacino said the drug should have similar effects in those patients. whether it would work in patients with brain injuries not caused by trauma, such as a stroke, isn’t known.

A neurologist who wasn’t involved in the research called it an important step. But many questions remain, including whether people less severely injured would benefit, and whether amantadine actually improves patients’ long-term outcome or just speeds up their recovery.

Dr. Ramon Diaz-Arrastia said the results were welcome news in a field that has seen many failed efforts. He is director of clinical research at the government’s Center for Neuroscience and Regenerative Medicine, which works with the military and government scientists on brain injury research.

“It’s an important step toward developing better therapies,” he said.

“Hope is critical and false hope is cruel for families dealing with this,” Susan Connors, president and chief executive of the Brain Injury Association of America, in Vienna, Va, told the New York Times. The new findings are “a little piece of hope, the real kind,” she said.

Since amantadine is commonly used, Diaz-Arrastia said U.S. troops with severe brain injuries in Iraq or Afghanistan probably get it, or should get it now. since 2000, some 233,000 troops have suffered traumatic brain injuries, including about 6,100 serious cases, many of them from bomb blasts or shrapnel.

The CDC has more on traumatic brain injury.