The purpose of the study is to evaluate how safe and how well SPD465 works compared to placebo in adults with ADHD. It is hypothesized that SPD465 will achieve an extended duration of clinical benefit.

Inclusion Criteria:

• Primary diagnosis of ADHD using DSM-IV-TR criteria (at least 6 of the 9 subtype criteria met)
• Baseline ADHD-RS-IV score =>24
• IQ score of => 80 (using Kaufman Brief Intelligence Test)

Exclusion Criteria:

• BMI < 18.5 or > 30 kg/m2
• Diagnosis of Post Traumatic Stress Disorder, psychosis, bipolar illness, severe obsessive compulsive disorder, severe depressive or severe anxiety disorder
• History of seizure disorder or a lifetime history of any seizures (other than infantile febrile seizures), any tic disorder, or a current diagnosis and/or family history of Tourette's Disorder
• History of uncontrolled hypertension or currently hypertensive
• Subjects who have taken atomoxetine (STRATTERA) within 30 days prior to screening
• Current (or history within the last 12 months) of drug dependence or substance abuse disorder according to DSM-IV-TR criteria (excluding nicotine)
• Female subject is pregnant or lactating, less than 3 months post partum