The present invention relates to the field of biomarkers and in particular to their utilisation in treatment. Embodiments of the invention have been particularly developed as biomarkers enabling optimisation of treatment regimes and as uses of the biomarkers in tests for the prediction of optimised treatments and treatment outcomes in the treatment of attention-deficit/hyperactivity disorder (ADHD) in children and adolescents. The invention will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.
