Evidence-based pharmacotherapy of attention deficit hyperactivity disorder

Introduction Attention deficit hyperactivity disorder (ADHD) is a neurobiological disorder, affecting significant numbers of children, adolescents, and adults worldwide. Research throughout the past century has established a strong scientific foundation for our current understanding of the etiology, epidemiology, and treatment of ADHD. The American Medical Association’s Council on Scientific Affairs in 1998 stated, “Overall, ADHD is one of the best-researched disorders in medicine, and the overall data on its validity are far more compelling than for many medical conditions” (Goldman et al., 1998). The American Academy of Child & Adolescent Psychiatry (AACAP), in their 2007 ADHD Practice Parameters concluded, “Although scientists and clinicians debate the best way to diagnose and treat ADHD, there is no debate among competent and well-informed healthcare professionals that ADHD is a valid neurobiological condition that causes significant impairment in those whom it afflicts” (Pliszka, 2007). Neuropsychological, neuroimaging, and genetic studies have demonstrated the biological underpinnings of ADHD. These studies have correlated deficits in executive functioning, response inhibition, delay aversion, vigilance, working memory, and planning with specific regions of the brain (Willcutt et al., 2005). Structural imaging studies have demonstrated that children with ADHD have significantly smaller brain volumes, on average, than same-aged comparison children (Castellanos & Tannock, 2002; Durston et al., 2004; Mostofsky et al., 2002), with smaller cerebellar and total cerebral volumes noted (Castellanos et al., 2002). In addition, functional imaging has revealed discrete variations in brain activation, specifically in the frontal-striatal cerebellar circuits (Krain & Castellanos, 2006). Family, twin, and more recently, genotyping studies provide further support for the biological basis of ADHD. There is considerable evidence that the principal cause of ADHD is genetic, with an estimated heritability of 76% (Faraone et al., 2005). Parents of children with ADHD are 2–8 times more likely to have the disorder themselves, and the risk is similar for siblings of affected children (Faraone & Biederman, 2000).