A Study to Evaluate Safety and Efficacy of ALKS 7290 Compared With Placebo in Adult Participants With Attention Deficit Hyperactivity Disorder (ALKS 7290-201)

Inclusion Criteria: * Meets the Diagnostic and Statistical Manual of Mental Disorders -5 criteria for ADHD, as confirmed by the Mini-International Neuropsychiatric Interview (MINI) for ADHD Studies 7.0.2. * Is otherwise healthy as determined by medical evaluation, including medical history, physical examination, laboratory tests, and cardiac monitoring. Participants must be stable on permitted medication for 2 months prior to first visit, without anticipated changes to dose. * AISRS total score of ≥26 * CGI-S score ≥ 4 (moderately ill or worse) * Has a Body Mass Index within 18 to 35 kg/m2 Exclusion Criteria: * Has a known history of intellectual developmental disorder or cognitive impairment that, in the opinion of the Investigator, would interfere with study participation. * Has any of the following psychiatric conditions per the DSM-5 criteria, as assessed by the MINI. Conditions not assessable by the MINI should be assessed by clinical judgement; Diagnosis of schizophrenia, schizoaffective disorder, or bipolar I or II disorder, or current, unstable, MDD or GAD. * Clinically significant cognitive difficulties including dementia, delirium or amnestic syndromes, or any other cognitive disorder present with the past 2 years that could interfere with participation in the study. * Moderate to severe substance use disorder according to DSM-5 guidelines, including use of alcohol, nicotine, cannabis, narcotics, or any illicit substance. * Any other psychiatric condition that could interfere with participation in the study.