DAT inhibitors, such as methylphenidate and the DAT substrate, amphetamine, are clinically used in the treatment of attention deficit hyperactivity disorders (ADHD) and modafinil and its R-enantiomer (armodafinil) are clinically approved for management of sleep disorders but also prescribed off-label for treatment of ADHD [15]. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.