The objective of this study is to compare the safety and efficacy of five doses of ABT-089 (2 mg QD, 5 mg QD, 15 mg QD, 40 mg QD and 40 mg BID) to placebo in adults with ADHD.

Inclusion Criteria:

• Meet criteria for attention deficit hyperactivity disorder
• Have voluntarily signed an informed consent form
• Are between 18 and 60 years of age
• Will use contraceptive methods during the study
• Women must not be pregnant or breast-feeding
• Must be in generally good health
• Are fluent in English

Exclusion Criteria:

• They have a current or past diagnosis of schizoaffective disorder, schizophrenia, obsessive-compulsive disorder, drug-induced psychosis, bipolar disorder, psychotic disorder or mental retardation
• They have a current diagnosis of major depressive episode, generalized anxiety disorder (GAD), or post-traumatic stress disorder (PTSD) or have a clinically significant sleep disorder requiring treatment
• They require ongoing treatment or expected treatment with any psychotropic medication, including anxiolytics, antipsychotics, anticonvulsants, antidepressants or mood stabilizers
• They failed to respond to two or more adequate trials of FDA-approved ADHD medication
• They have violent, homicidal or suicidal ideation
• They have a significant history of medical diagnoses, seizure disorder, Tourette's syndrome or a central nervous system (CNS) disease, excluding ADHD
• They have a urine drug screen that is positive for alcohol or drugs of abuse
• They have a history of substance or alcohol disorder (abuse/dependence) during the last 3 months