The safety and effectiveness of the drug, a selective serotonin and norepinephrine dual reuptake inhibitor, were established in clinical trials involving 2,084 patients. In a news release, the drug's makers said it's not known exactly how Savella improves symptoms of fibromyalgia, which some scientists believe is related to abnormalities in certain brain neurotransmitters.

As many as 6 million Americans have fibromyalgia, making it the second-most common condition diagnosed in rheumatology clinics behind osteoarthritis, the companies said. There is no cure.

Savella is expected in pharmacies by March. Common side effects reported during clinical testing included constipation, hot flushes, vomiting, heart palpitations, dry mouth, and a rise in blood pressure.

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