1. To judge if the patient is a responder to ADHD drugs the SNAP-IV rating of ADHD symptoms (before and after medication start) is used. The patients who at 3 months have an at least 40% reduction in SNAP-IV score are reckoned "responders" and those who at the same time point have a less than 20% change in SNAP-IV score are reckoned "non-responders". Differences between the groups will be analyzed with logistic regression, with responder status as depending variable, and genotype and the other risk markers (biological, phenotypic, and psychosocial markers) as independent variables after correction for symptoms at baseline. Even a 50% drop-out rate will (i.e. 1000 out of estimated 2000 eligible individuals) give a 98% power to identify a 49% increase in non-responder proportion for a specific genotype.