Philippe Robaey, as Principal Investigator, is a physician and child Psychiatrist and Director of the ADHD clinic at CHEO. He has many years of clinical and research experience with MPH. Dr. Robaey will be responsible for the medical aspects of the study such as prescribing the study medication under double blind conditions, as well as overseeing the evaluation of vital sign and side effects of MPH. Dr. Eric Doucet, as Co-Principal Investigator (C0-PI) is a Full Professor of Human Kinetics at University of Ottawa, Faculty of Health Sciences. Dr. Doucet is an expert in the measurement of energy balance measures using the proposed methods. The study of the adult population will be conducted in Dr. Doucet's Behavioural Metabolic Research Unit, where our previous MPH cross-over trial was done, and he will oversee the coordination and supervision of the experimental testing procedures. Dr. Gary Goldfield, as Co-Principal Investigator (CO-PI), is a clinical psychologist and Investigator with the Healthy Active Living and Obesity Research Group at the CHEO Research Institute. He will oversee the assessment of psychiatric inclusion criteria evaluated by questionnaire and structured clinical interview, as well as the measurement of the reinforcing (rewarding) value of food. Dr. Jameason Cameron, as co-Principal investigator, is a postdoc and a research coordinator at CHEO. He has extensive experience with feeding studies and weight loss trials, and measures of food reward and smell function. Dr. Cameron will be responsible for the day-to-day testing and to supervise the PhD student who will be co-coordinating the study.