Tipepidine in Children With Attention Deficit/Hyperactivity Disorder (AD/HD): a Double-blind, Placebo-controlled Trial

\[Inclusion Criteria\] 1. Diagnosis of attention deficit hyperactivity disorder besed on DSM-5 criteria. 2. Scores of 20 or higher in ADHD-RS (physician evaluation) total score. 3. currently is an outpatient at Chiba University Hospital Department of Psychiatry or Child Psychiatry. 4. currently receiving no medications for ADHD (atomoxetine, methylphenidate) treatment for the previous 4 weeks prior to enrollment in this study. 5. currently receiving no medications of antidepressants, mood stabilizers and the antipsychotics treatment for the previous 4 weeks prior to enrollment in this study. 6. currently receiving no medications of GIRK channel antagonist (tipepidine, cloperastine, caramiphen) treatment for the previous 4 weeks prior to enrollment in this study. 7. Ages 6 - 17, male or female 8. Provision of written informed consent by patients and parents or guardian. 9. must be able to swallow capsuled medicine. \[Exclusion Criteria\] 1. History of allergic reaction or hypersensitivity to tipepidine hibenzate. 2. Patients who have not been informed of having the disease at the time of informed consent. 3. Diagnosis of any of the following diseases based on the DSM-5 criteria. Autism Spectrum Disorder, Schizophrenia Spectrum and Other Psychotic Disorders, Neurocognitive Disorders, Substance Related and Addictive Disorders, Feeding and Eating Disorders, Personality Disorders, Paraphilic Disorders. 4. currently receiving medications for ADHD (atomoxetine, methylphenidate) treatment for the previous 4 weeks prior to enrollment in this study. 5. currently receiving medications of antidepressants, mood stabilizers and the antipsychotics treatment for the previous 4 weeks prior to enrollment in this study. 6. currently receiving medications of GIRK channel antagonist (tipepidine, cloperastine, caramiphen) treatment for the previous 4 weeks prior to enrollment in this study. 7. Somatic disorder which requires severe body management or severe meal management. 8. participating in another clinical trial within 3 months prior to enrollment into this study. (except for observation study without intervention). 9. planning change of treatment because of unstable neurological manifestations or somatic symptoms. 10. History of suicidal ideation within the past year. 11. pregnant or nursing, or intending to become pregnant or to start breastfeeding during the study. 12. Other clinically significant reasons for exclusion by investigators.