Previous human studies reported the associations between the different polymorphisms in the gene coding for 5-HT1B and alcohol dependence [15,16], alcohol abuse [17], aggressive behaviour [18,19], anger and hostility [20], attention-deficit/hyperactivity disorder (ADHD) [21], substance abuse [22], and schizophrenia [23,24]. This evidence concerns the gene HTR1B and attention deficit-hyperactivity disorder.