SLC6A3 and attention deficit-hyperactivity disorder: MPH has been shown superior to placebo in providing symptom relief in ADHD (Epstein et al. 2014; Faraone and Buitelaar 2010), and is believed to exert its effect by inhibiting the dopamine transporter (encoded by DAT/SLC6A3 gene) and/or the noradrenaline transporter (encoded by NET/SLC6A2 gene) (Engert and Pruessner 2008).