A Study to Test Different Ways to Measure the Effect of Atomoxetine on Impulsive Behavior in Young Adults With Attention Deficit Hyperactivity Disorder (ADHD)

Inclusion criteria * Male and female subjects, 18-45 years of age at the time of consent meeting diagnostic criteria of Attention Deficit Hyperactivity Disorder (ADHD) per Diagnostic and Statistical Manual of Mental Disorders (DSM-5) at screening visit and currently undergoing diagnostic assessment and/or treatment for ADHD * Signed and dated written informed consent in accordance with ICH-GCP and local legislation prior to admission to the trial. * A diagnosis of the moderate symptoms of ADHD confirmed with combined score of 4 or higher in Clinical Global Impression-ADHD-Severity (CGI-ADHD-S) at Screening; Hyperactivity/Impulsivity subscale min 8 (at least moderate for impulsivity measure with ADHD checklist) * Able and willing to discontinue the use of any psychotropic medications for treatment of ADHD symptoms, as well as of all relevant co-medication for comorbid conditions during the study * Women of childbearing potential (WOCBP) \[1\] must be ready and able to use highly effective methods of birth control per ICH M3 (R2) that result in a low failure rate of less than 1% per year when used consistently and correctly. A list of contraception methods meeting these criteria and instructions on the duration of their use is provided in the patient information. 1. A woman is considered of childbearing potential (WOCBP), i.e. fertile, following menarche and until becoming post-menopausal unless permanently sterile. Permanent sterilisation methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. Tubal ligation is NOT a method of permanent sterilisation. Exclusion criteria * Per DSM-5, had ever met diagnostic criteria for schizophrenia, schizoaffective disorder, schizophreniform disorder, bipolar disorder, delusional disorder or major depressive disorder (MDD) with psychotic features at the time of screening. * Diagnosis of any mental disorder (according to DSM-5) that was primary focus of treatment within 6 months prior to Screening or at Baseline (as per clinical discretion of the investigator). --The following are not excluded: Substance Induced Mood Disorder, Major Depressive Disorder in remission, Generalized Anxiety Disorder in remission, Post-Traumatic Stress Disorder in remission, recreational/occasional substance use as long as willing to stop for duration of the study, Borderline Personality Disorder. * Any psychiatric disorder, including the ones mentioned under #1, that in the opinion of the investigator would compromise participants' safety and/or validity of the data. * Current or recent (in the 6 months prior to screening) suicidal ideation or behaviour of type 4 or 5 in the Columbia Suicidal Severity Rating Scale (C-SSRS). * Any finding in the medical examination (including blood pressure (BP), pulse rate (PR), temperature, or Electrocardiogram (ECG)) deviating from normal and assessed as clinically relevant by the investigator. * Repeated measurement of systolic blood pressure outside the range of 90 to 145 millimetre of mercury (mmHg), diastolic blood pressure outside the range of 45 to 90 mmHg, or pulse rate outside the range of 45 to 95 beats per minute (bpm). * A marked baseline prolongation of QT/QTc interval (\[QT/QTc = Time between start of the Q-wave and the end of the T-wave in an electrocardiogram / QT interval corrected for heart rate using the method of Fridericia (QTcF) or Bazett (QTcB)\] such as QTc intervals that are repeatedly greater than 450 milliseconds (ms) in males or repeatedly greater than 470 ms in females) or any other relevant electrocardiogram (ECG) finding at screening. * A history of additional risk factors for Torsade de Pointes (such as heart failure, hypokalaemia, or family history of Long QT Syndrome). * Further exclusion criteria apply