A mysterious condition that causes pains and chronic flu-like symptoms and exhaustion may be eased by a cheap drug that has been around for 30 years.

Researchers at Stanford University said that a small study showed that naltrexone, which has been used to treat drug addiction, reduced the pain of fibromyalgia 30 percent more than a placebo.

The results were based on a small study of 10 women who were studied for 14 weeks. They were given a placebo part of the time and the drug at other times, but they did not know which they were taking.

"Patients' reactions were really quite profound," said author Dr. Sean Mackey. "Some people decided to come off other medications. Some people went back to work really improving their quality of life."

He emphasized that the early results were not enough to lead to a recommendation, but said he hopes larger studies would give more information.

There are few treatments for fibromyalgia, but this one would only cost about $40 a month, according to a news release on the work.

While the diagnosis is still controversial because there is no definitive way to test for it, some say that 4 percent of people in the U.S. have the condition.

Jarren Younger, another author of the study, said the idea to test the drug came when people in support groups said it had worked for them.

The study will be published April 17 in the journal Pain Medicine.