The primary purpose of this study is to evaluate the efficacy, safety, and tolerability of 40 mg per day of istradefylline (KW6002) in patients with Restless Legs Syndrome.

Restless Legs Syndrome (RLS) is a very common neurological disorder with a prevalence of approximately 10% in the adult population. It is characterized by an almost irresistible urge to move the legs, usually accompanied by feelings of intense discomfort. The feelings are usually present while at rest and are temporarily relieved by activity. Symptoms are worse in the evening and at night and lead to profound sleep disturbance and daytime fatigue.

Although a number of therapeutic approaches have been used to treat the symptoms of RLS, none have been universally adopted. While it has been shown that some dopaminergic anti-parkinsonian medications are effective in treating RLS, their use may be somewhat limited by side effects associated with long-term dopaminergic activation. Istradefylline may provide a nondopaminergic approach to the treatment of RLS.

This study will compare the efficacy of 40 mg per day of istradefylline in improving the symptoms of RLS with placebo.

Inclusion Criteria:

RLS that is mild to moderate in severity, non-nursing and non-pregnant if female, with an otherwise normal examination.

Exclusion Criteria:

Unable to stop other RLS medication, treatment with excluded medications, abnormal medical status.