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.