Attention-deficit/hyperactivity disorder (ADHD) is a common neuropsychiatric disorder of inattention, hyperactivity, and impulsivity. Roles for dopamine and norepinephrine are widely recognized; however, the role of serotonergic neurotransmission is less clear. This systematic literature review aimed to determine if changes in serotonin transmission are implicated in the neurobiology of ADHD. A search of published literature was conducted. Eligible publications addressing the role of serotonin, its receptor family, and/or its transporter in the neurobiology of ADHD were selected according to prespecified criteria. The quality of evidence was graded. Of 95 publications meeting our criteria, many (n = 60) were nonclinical studies. Most publications were rated as containing medium- (62.1%) or high-grade (17.9%) evidence. Multiple strands of evidence were found to implicate serotonin in ADHD, with 81.1% of the identified articles providing support for altered levels of serotonin production, binding, transport, or degradation in ADHD. Substantial evidence implicates serotonin in the neurobiology of ADHD and in the regulation of the catecholaminergic systems believed to be dysregulated by the disorder. Yet this evidence is incomplete and, at times, conflicting. It does suggest, however, that medications that engage the serotonin system should be tested for their efficacy in the treatment of ADHD.
Faraone et al. (Tue,) studied this question.