<qa>  What is the primary objective of the study?The primary objective of this study is to evaluate the maintenance of efficacy, as measured by Adult ADHD Rating Scale with Prompts Adult ADHD-RS with prompts and Clinical Global Impression - Severity CGI-S scores, through a randomized withdrawal design when subjects with ADHD have been on stable treatment with commercial SPD489 for a minimum of 6 months and are maintained on their screening dose of commercial SPD489. 