The purpose of this study is to test if the investigational medication ABT-089 is a safe and effective treatment for adults with Attention-Deficit/Hyperactivity Disorder (ADHD).

Inclusion Criteria:

• Have voluntarily signed an informed consent form.
• Meet diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD) based on detailed evaluation and interview with subject.
• Subject is generally in good health based on medical history, physical examination, clinical lab tests and ECG.
• Female subjects of child-bearing potential must have a negative urine pregnancy test at screening and baseline and agree to comply with applicable contraceptive requirements.
• Male subjects must agree to comply with applicable contraceptive requirements.
• Subject is able to keep required appointments for clinic visits and all tests, including blood draws and examinations.

Exclusion Criteria:

• Subject has a current or past diagnosis of schizoaffective disorder, schizophrenia, obsessive-compulsive disorder, drug-induced psychosis, bipolar disorder, psychotic disorder.
• Current diagnosis of major depressive disorder, generalized anxiety disorder, PTSD or has a sleep disorder requiring treatment of any kind.
• Subject has a history of, or ongoing, serious medical problem.
• Subject has a history of significant allergic reaction to any drug.
• Subject is planning to begin any type of behavioral or psychotherapy for treatment of ADHD.
• Subject requires ongoing treatment with any psychiatric medication.