FM is a chronic and debilitating condition characterized by widespread pain and stiffness throughout the body, accompanied by severe fatigue, insomnia and mood symptoms. Unlike arthritis and other debilitating rheumatological disorders, FM produces serious and chronic pain that is not the result of inflammation. Pain associated with FMS is of a "head-to-toe" nature, and is described as a diffuse aching or burning. Pain can vary in severity and location from day to day and, in some people, it can be so intense that it interferes with the performance of even simple tasks, while in others it may cause only moderate, ongoing discomfort. By some measures, patients with FM have at least comparable disability, more pain and lower quality of life than patients with rheumatoid arthritis or osteoarthritis. Although FM has been medically recognized for many years, it was only in 1990 that medical specialists agreed on the signs and symptoms that must be present to make the diagnosis. The American College of Rheumatology, or ACR, diagnosis criteria for FM include a history of widespread and longstanding pain, as measured by pain upon application of pressure in 11 of 18 designated tender points. Specialists in the field of FM have concluded that FM is a result of a generalized and heightened perception of sensory stimuli resulting from abnormal pain processing within the central nervous system, and in most instances, is triggered by physical trauma, emotional stress or infection.

According to the American College of Rheumatology, FM is estimated to affect over six million people in the United States. A recent scientific article suggests that because the ACR criteria were designed for clinical research purposes and therefore limit the FM diagnosis, the 2-4% prevalence may under-represent the actual prevalence of chronic widespread pain in the population. Most FM patients are middle-aged women, although the ailment can strike children, the elderly and men. According to the ACR, FM is diagnosed four times more frequently in women than in men and once symptoms appear, most patients can expect to suffer the condition throughout their entire life. As a result of the diversity of symptoms, there are numerous physician specialties involved in the treatment and management of FM. FM is most often diagnosed in the primary care setting and, in addition, is the second most commonly diagnosed condition in rheumatology clinics in the United States after osteoarthritis.

Despite the high prevalence and severity of this syndrome, there are limited treatment options specifically approved for FM in the United States or elsewhere (the first drug was approved for FM in June 2007), and the addressable patient population is not yet well established. Current treatments consist of a regimen that includes medication to diminish pain and improve sleep, exercise programs that stretch muscles and improve cardiovascular fitness and physical therapy and relaxation techniques to ease muscle tension. Antidepressants are often prescribed for FM patients, as low doses of these medications appear to relieve pain associated with FM. Tricyclic antidepressants, or TCAs, a class of compounds that are known to be effective analgesics, or pain-reducing drugs, in multiple chronic pain conditions, including FM, are currently viewed as one of the class of drugs of choice in treating FM. TCAs, however, are severely limited in their use for the treatment of FM because they have been linked with side effects such as arrhythmias, the risk of fatal overdose, as well as contributing to weight gain and drowsiness, which is particularly problematic because individuals with FM are already suffering from fatigue.