We have been engaged as investigators and national coordinators in several international multi-centre randomised placebo-controlled trials (RCTs) of newly developed medications for ADHD in children and adolescents, trials which have served as a basis for the approval of these medications in Europe. We performed an RCT of Omega 3/6 treatment for children and adolescents with ADHD (2009), and an RCT of Omega 3/6 for reading ability in mainstream schoolchildren (2016). We did a small open pilot trial (2012) of a cognitive training method “Collaborative Problem Solving, CPS” for children and adolescents with ADHD and severe irritability/problem behaviours, and have recently completed a large RCT (under review for publication 2020) with a modified form of this method (Problem Resolution for ESSENCE; PR-ESSENCE) for children with autism and/or ADHD with similar severe problems. A large open trial of long-term (2 years) medication for ADHD is underway, looking at effectiveness in improving ADHD symptoms, functioning in school, family, with friends, in everyday activities, and quality of life. We have recently completed an observational cohort study investigating the phenotype of children and adolescents with a suspected neuroinflammatory condition called “Paediatric Acute-onset Neuropsychiatric Syndrome, PANS”.