A low dose of naltrexone, a drug commonly used to treat alcoholism and drug addiction, is effective in relieving pain and fatigue in some patients with fibromyalgia, researchers from Stanford University School of Medicine in Palo Alto, California have found.

Fibromyalgia is characterized by chronic pain, fatigue and difficulty sleeping. It's a somewhat mysterious condition with no clear-cut cause or treatment.

In a small study, naltrexone was found to reduce symptoms of pain and fatigue an average of 30 percent over placebo, according to a report in the journal Pain Medicine.

"Patients' reactions were really quite profound," lead investigator Dr. Sean Mackey, chief of the pain management division at Stanford University Medical Center, noted in a university-issued statement. "Some people decided to come off other medications. Some people went back to work really improving their quality of life."

Still, it's too early to recommend naltrexone for fibromyalgia sufferers. "While we're excited about preliminary results, they are still preliminary," Mackey said, "and we need to do longer studies with more patients. There is still a significant amount of work to be done."

In the study of 10 patients with fibromyalgia, the severity of fibromyalgia symptoms was reduced by 32.5 percent with naltrexone compared with only 2.3 percent with placebo. Naltrexone treatment at bedtime also significantly reduced daily pain, highest pain, fatigue, and stress, and significantly improved pain "thresholds."

Six patients were classified as responders, with a 30 percent greater reduction of fibromyalgia symptoms during naltrexone compared with placebo.

The study team is moving ahead with a second, longer-term trial of 30 patients who will be tested during a 16-week period.

Low-dose naltrexone is particularly promising, the researchers say, because of the few treatment options available for fibromyalgia patients, its low cost of about $40 a month and its limited side effects. Vivid dreams were reported by a few participants.