To evaluate maintenance of efficacy based on time to relapse between SPD489 (50 or 70mg) and placebo, as measured by the number of binge days (defined as days during which at least 1 binge episode occurs) per week as assessed by clinical interview based on subject diary and Clinical Global Impression - Severity (CGI-S) scores for patients who responded to SPD489 by the end of the Open-label Treatment Phase.