The purpose of this study is to evaluate the long-term safety of SPD489 administered as a daily morning dose (5, 10, 15, 20, and 30 mg/day) in preschool children diagnosed with Attention-deficit/Hyperactivity Disorder (ADHD).

This study is a long-term, open-label study where participants who participated in an antecedent SPD489 study (SPD489-211 [NCT02402166] or SPD489-347 [NCT03260205]) or through direct enrollment. Participants entering into this study will be classified as either a roll-over participants or a direct-enrolled participants.

Inclusion Criteria:

1. Participant is male or female aged 4-5 years inclusive at the time of consent from antecedent studies SPD489-211 or SPD489-347 or at the time of consent if directly enrolled.

2. Before completing any study-related procedures, participant's parent(s) or legally authorized representative (LAR) must provide signature of informed consent, and there must be documentation of assent (if applicable) by the participant indicating that the participant is aware of the investigational nature of the study. The participant's parent(s) or LAR should understand that the required procedures and restrictions are being conducted in accordance with the International Council of Harmonisation (ICH) Good Clinical Practice (GCP) Guideline E6 (1996), any updates or revisions, and applicable federal or local regulations.

3. Participant and parent(s)/LAR are willing and able to comply with all of the testing and requirements defined in the protocol, including oversight of morning dosing. Specifically, the parent/LAR should be available at approximately 7:00AM (+2 hours) to dispense the dose of investigational product for the duration of the study.

4. Roll-over participant from antecedent SPD489-347 study:

   a. Participant completed the antecedent study (SPD489-347)

5. Direct enrolled participants must meet antecedent study inclusion criteria, as listed below

   1. Participant must meet Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV-TR) criteria for a primary diagnosis of ADHD (any subtype) based on a detailed psychiatric evaluation conducted by a sponsor-approved clinician
   2. Participant has an attention-deficit/hyperactivity disorder rating scale- IV (ADHD-RS-IV) Preschool Version total score at the Baseline Visit (Visit 0) of greater than equals to (>=) 28 for boys and >= 24 for girls.
   3. Participant has a Clinical Global Impressions - Severity of Illness (CGI-S) score >=4 at the Baseline Visit (Visit 0).
   4. Participant has a Peabody Picture Vocabulary Test, Fourth Edition standard score of >=70 at the Screening Visit (Visit -1).
   5. Participant has undergone an adequate course of non-pharmacological treatment based on investigator judgment or the participant has a severe enough condition to consider enrollment without undergoing prior non-pharmacological treatment, based on investigator judgment.
   6. Participant has, in the opinion of the investigator, participated in a structured group activity (eg, preschool, sports, Sunday school) so as to assess symptoms and impairment in a setting outside the home.
   7. Participant has lived with the same parent(s) or guardian for >=6 months.

Exclusion Criteria:

1. Participant was terminated from an antecedent SPD489 study for non-compliance and/or experienced a serious adverse event (SAE) or adverse event (AE) resulting in termination.

2. Participant is required to or anticipates the need to take medications that have central nervous system effects or affect performance, such as, but not limited to, sedating antihistamines and decongestant sympathomimetics, or monoamine oxidase inhibitors. Stable use of bronchodilator inhalers is not exclusionary.

3. Participant has a concurrent chronic or acute illness (such as, but not limited to, severe allergic rhinitis or an infectious process requiring antibiotics), disability, or other condition that might confound the results of safety assessments conducted in the study or that might increase risk to the participant. Similarly, the participant will be excluded if he or she has any additional condition(s) that, in the investigator's opinion, would prohibit the participant from completing the study or would not be in the best interest of the participant. The additional condition(s) would include any significant illness or unstable medical condition that could lead to difficulty complying with the protocol. Mild, stable asthma is not exclusionary.

4. Participant has a documented allergy, hypersensitivity, or intolerance to amphetamine or to any excipients in the investigational product.

5. Participant has a known family history of sudden cardiac death or ventricular arrhythmia.

6. Participant has a blood pressure measurement >= 95th percentile for age, sex, and height at the screening visit (Visit -1) or the baseline visit (Visit 0) or a history of moderate or severe hypertension.

7. Participant has a known history of symptomatic cardiovascular disease, unexplained syncope, exertional chest pain, advanced arteriosclerosis, structural cardiac abnormality, cardiomyopathy, serious heart rhythm abnormalities, coronary artery disease, or other serious cardiac problems placing them at increased vulnerability to the sympathomimetic effects of a stimulant drug.

8. Participant is taking any medication that is excluded per the protocol.

9. Participant had any clinically significant electrocardiogram (ECG) or clinical laboratory abnormalities at the Screening Visit (Visit -1) or baseline visit (Visit 0), based on investigator judgment.

10. Participant has a history of hyperthyroidism, or current abnormal thyroid function, defined as abnormal thyroid stimulating hormone (TSH) and thyroxine (T4) at the Screening Visit (Visit-1) or Visit 0. Treatment with a stable dose of thyroid medication for at least 3 months is permitted.

11. Participant has taken another investigational product or has taken part in a clinical study within 30 days prior to the Screening Visit (Visit -1).

12. Participant is well-controlled on his/her current ADHD medication with acceptable tolerability.

13. Participant has glaucoma.

14. Participant has failed to fully respond, based on investigator judgment, to an adequate course of amphetamine therapy.

15. Participant has a current, controlled (requiring medication or therapy) or uncontrolled, comorbid psychiatric disorder including but not limited to any of the below co-morbid Axis I disorders and Axis II disorders:

    1. post-traumatic stress disorder (PTSD) or adjustment disorder
    2. bipolar illness, psychosis, or family history of these disorders
    3. pervasive developmental disorder
    4. obsessive-compulsive disorder (OCD)
    5. psychosis/schizophrenia
    6. participant has a serious tic disorder, or a family history of Tourette's disorder
    7. participant is currently considered a suicide risk in the opinion of the investigator, has previously made a suicide attempt, or has a prior history of, or is currently demonstrating active suicidal ideation. Participants with intermittent passive suicidal ideation are not necessarily excluded based on the assessment of the investigator
    8. a history of physical, sexual, or emotional abuse
    9. any other disorder or agitated state that in the opinion of the investigator, contraindicates SPD489 or lisdexamfetamine dimesylate treatment or confound efficacy or safety assessments.

16. Participant has initiated behavioral therapy within 1 month of the baseline visit (Visit 0). Participant may not initiate behavioral therapy during the study.

17. Participant has a height <=5th percentile for age and sex at the screening visit (Visit -1).

18. Participant has a weight <=5th percentile for age and sex at the screening visit (Visit -1).

19. Participant lives with anyone who currently abuses stimulants or cocaine.

20. Participant has a history of seizures (other than infantile febrile seizures).

Takeda provides access to the de-identified individual participant data (IPD) for eligible studies to aid qualified researchers in addressing legitimate scientific objectives (Takeda's data sharing commitment is available on https://clinicaltrials.takeda.com/takedas-commitment?commitment=5). These IPDs will be provided in a secure research environment following approval of a data sharing request, and under the terms of a data sharing agreement.

IPD from eligible studies will be shared with qualified researchers according to the criteria and process described on https://vivli.org/ourmember/takeda/. For approved requests, the researchers will be provided access to anonymized data (to respect patient privacy in line with applicable laws and regulations) and with information necessary to address the research objectives under the terms of a data sharing agreement.