OBJECTIVE:This study examined the time course of efficacy-related endpoints for lisdexamfetamine dimesylate (LDX) versus placebo in adults with protocol-defined moderate to severe binge-eating disorder (BED). METHODS:In two 12-week, double-blind, placebo-controlled studies, adults meeting DSM-IV-TR BED criteria were randomized 1:1 to receive placebo or dose-optimized LDX (50 or 70 mg). Analyses across visits used mixed-effects models for repeated measures (binge eating days/week, binge eating episodes/week, Yale-Brown Obsessive Compulsive Scale modified for Binge Eating [Y-BOCS-BE] scores, percentage body weight change) and chi-square tests (Clinical Global Impressions-Improvement [CGI-I; from the perspective of BED symptoms] scale dichotomized as improved or not improved). These analyses were not part of the prespecified testing strategy, so reported p values are nominal (unadjusted and descriptive only). RESULTS:Least squares mean treatment differences for change from baseline in both studies favored LDX over placebo (all nominal p values <  .001) starting at Week 1 for binge eating days/week, binge-eating episodes/week, and percentage weight change and at the first posttreatment assessment (Week 4) for Y-BOCS-BE total and domain scores. On the CGI-I, more participants on LDX than placebo were categorized as improved starting at Week 1 in both studies (both nominal p values <  .001). Across these efficacy-related endpoints, the superiority of LDX over placebo was maintained at each posttreatment assessment in both studies (all nominal p values <  .001). DISCUSSION:In adults with BED, LDX treatment appeared to be associated with improvement on efficacy measures as early as 1 week, which was maintained throughout the 12-week studies.