Introduction

Taken together, the data presented in the previous two chapters paint a clear picture of attention deficit hyperactivity disorder (ADHD) as a highly prevalent, heterogeneous, and oftentimes lifelong neurobehavioral disorder that results in considerable functional impairment for afflicted individuals. Further, while efficacious treatments are available, most provide limited long-term benefits. As discussed in the prior chapters, ADHD is quite prevalent in childhood, making it more the rule than the exception that classrooms will have at least one child with the disorder. Prevalence rates are generally estimated to be lower among adults, but it is this group that is beginning to be clinically referred and identified at much higher rates in recent years, and this primarily accounts for the substantial increase in medication prescriptions written to treat ADHD. Yet knowledge regarding continuity between the childhood, adolescent, and adult conditions in ADHD remains quite limited.

That ADHD is a heterogeneous disorder is generally well accepted throughout the scientific literature, and these multiple sources of variability are problematic for the diagnosis, study, and treatment of ADHD. This heterogeneity is perhaps most apparent phenomenologically with regard to the core defining symptom domains, as evidenced by the three distinct subtypes (predominantly inattentive [ADHD-I], predominantly hyperactive/impulsive [ADHD-HI], and combined [ADHD-C]), as well as with regard to associated features and comorbidities. As described in the previous chapters, it is the exception rather than the rule when an individual with ADHD does not meet criteria for at least one other psychiatric disorder and/or a learning disability.