LONDON (Reuters) - Antidepressants appear to relieve pain, sleep disturbances and other symptoms of fibromyalgia, a debilitating and painful ailment with no known cure, German researchers said on Tuesday.

A range of antidepressants look to improve quality of life for people with the condition that affects up to an estimated 6 percent of people in North America and Europe, they added.

"Fibromyalgia syndrome is also associated with high direct and indirect disease-related costs," Winfried Hauser of Klinikum Saarbrucken in Germany and colleagues wrote in the Journal of the American Medical Association.

"Effective treatment of fibromyalgia syndrome is therefore necessary for medical and economic reasons."

The condition mainly strikes women and can cause severe pain and tenderness in muscles, ligaments and tendons. Shoulder and neck pain is common but some people with the ailment also have problems sleeping, and suffer anxiety and depression.

Doctors usually prescribe exercise and relaxation techniques, painkillers or sometimes a low-dose antidepressant to treat the symptoms.

Pregabalin, a drug that calms nerve cells, gained U.S. regulatory approval last year to treat the condition. It is sold as Lyrica by Pfizer Inc.

Hauser and colleagues analysed 18 previously published studies involving 1,427 participants and found strong evidence antidepressants led to improved symptoms and quality of life.

Older tricyclic and tetracyclic antidepressants seemed to have a large effect in easing pain, fatigue and sleep disturbances while selective serotonin reuptake inhibitors (SSRIs) such as Prozac had smaller effect for pain relief.

Prozac was initially introduced by U.S. drugmaker Eli Lilly and Co in 1987 and is now off patent and widely available generically as fluoxetine.

A newer class of treatments called serotonin and noradrenaline reuptake inhibitors (SNRIs) were linked to a reduction of pain, sleep disturbances and depressed mood, and monoamine oxidase inhibitors appeared to help reduce pain.

While the analysis suggests antidepressants may help, the researchers said doctors should closely monitor people using them because there is a lack of evidence about their long-term impact.

"Their effects should be re-evaluated at regular intervals to determine whether benefits outweigh adverse effects," the researchers wrote.

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