Safety and Efficacy Study of SHP465 in Adults Aged 18-55 Years With Attention-deficit/ Hyperactivity Disorder (ADHD)

Inclusion Criteria: Subject must be 18-55 years of age Subject is able to provide written, personally signed and dated informed consent. Subject is willing and able to comply with all of the testing and requirements defined in the protocol Subject, who is a female, must not be pregnant. Subject must have a satisfactory medical assessment with no clinically significant or relevant abnormalities. Subject has a primary diagnosis of ADHD. Subject has an adult ADHD-RS with prompts total score ≥28 at the baseline visit. Subject must have a minimum level of intellectual functioning, as determined by the investigator. Subject is able to swallow a capsule. Subject is currently not on ADHD therapy or is not completely satisfied with any aspect of their current ADHD therapy. Exclusion Criteria: Subject has a current, comorbid psychiatric diagnosis with significant symptoms. Subject is considered a suicide risk in the opinion of the investigator Subject has a body mass index (BMI) of \<18.5 kg/m2 at the screening visit. Subject has a BMI ≥40 kg/m2 at the screening visit. Subject has a concurrent chronic or acute illness, disability, or other condition. Subject has a history of seizure, a chronic or current tic disorder, or a current diagnosis of Tourette's disorder. Subject has a history of moderate to severe hypertension. Subject has a known history of symptomatic cardiovascular disease Subject has a known family history of sudden cardiac death or ventricular arrhythmia. Subject has any clinically significant ECG or clinically significant laboratory abnormality at the screening visit. Subject has current abnormal thyroid function Subject has a documented allergy, hypersensitivity, or intolerance to amphetamine or to any excipients in the investigational product. Subject has failed to respond, to an adequate course(s) of amphetamine therapy. Subject has a history of suspected substance abuse or dependence disorder. Subject has a positive urine drug result at the screening visit (with the exception of subject's current stimulant therapy, if any) or Subject has taken another investigational product or has taken part in a clinical study within 30 days prior to the screening visit. Subject has previously completed, has discontinued, or was withdrawn from this study. Subject is taking any medication that is excluded or has not been appropriately washed out according to the protocol requirements. Subject is required to take or anticipates the need to take medications that have CNS effects or affect performance. Subject is female and is pregnant or lactating.