This study examined the clinical efficacy, tolerability and safety of CX717 in the treatment of adults with ADHD. The study was a double-blind, 2-period crossover study that compared 2 different doses of CX717 with placebo. Subjects were randomized to 1 of 4 different treatment sequences: placebo - low dose; low dose - placebo; placebo - high dose; or high dose - placebo. Each treatment period was 3 weeks with a 2-week washout between treatment periods. The doses chosen were 200 mg b.i.d. and 800 mg b.i.d.