In the United States, attention-deficit/hyperactivity disorder (ADHD) is the most common neuropsychiatric disorder afflicting children and adolescents. Epidemiologic studies in the United States indicate that approximately 5% of youths have ADHD.1 ADHD is characterized by the childhood onset of symptoms of inattention, distractibility, impulsivity, and motor hyperactivity that occur in more than one domain of functioning (e.g., home, work, school, socially). Symptoms must be debilitating and impair life functioning.
Current diagnostic criteria for ADHD describe three subtypes: hyperactive-impulsive, inattentive, and combined. The combined subtype is the most common.2 Boys predominate in an approximately 3:1 ratio, but evidence suggests that girls with ADHD, who may be more likely to have the inattentive subtype, are underdiagnosed and undertreated more often in comparison to boys.
Recent population prevalence studies indicate that ADHD is also quite common and impairing in adults. Indeed, studies indicate that 60% or more of children with ADHD will continue to exhibit debilitating symptoms, if not meet full syndrome criteria, into adulthood.3 Such high persistence rates of ADHD into adulthood and its associated impairments (affecting functioning in educational attainment, employment, social and marital relationships, driving, and overall life functioning) have received increased clinical and research attention in recent years.
The recently published National Comorbidity Survey Replication study reported that approximately 4.4% of U.S. adults (i.e., 7 million) suffer from debilitating symptoms of ADHD.4 Adult rates indicate a 1.6:1 ratio favoring males over females. The impact of ADHD and associated consequences of symptoms of inattention, hyperactivity, and impulsivity may be even greater in adulthood than in childhood. Adults with ADHD were found to have elevated rates of disability in basic life functioning and were more likely to be unemployed or divorced, yet only 10.9% had received treatment for their ADHD symptoms in the previous year.4 This rate of treatment is strikingly low in comparison to rates for other psychiatric disorders, such as anxiety, mood, or substance use disorders, and it reflects the significant problems of underrecognition and undertreatment of adult ADHD. Clinical studies of adult ADHD indicate that the disorder is more heterogeneous, and the symptoms subtler, in adults than in children, which may partially explain why the disorder is largely underrecognized in adults.5
Complicating ADHD's clinical picture is the fact that as many as 50% of individuals with the disorder will meet the criteria for at least one comorbid psychiatric condition.4,6,7 In children these coexisting conditions include learning disabilities, anxiety disorders, mood disorders, autism spectrum disorders, and other disruptive behavioral disorders such as oppositional defiant disorder and conduct disorder. These disorders have an obvious impact on children's abilities to function adequately in their academic, social, and family environments and, in combination with ADHD symptoms, often lead to adverse life outcomes and increased utilization of mental health, academic, and criminal justice system resources.
In adolescents and adults, mood and anxiety disorders, as well as substance abuse disorders, commonly coexist with ADHD.8 Mood disorders, anxiety, substance use, and intermittent explosive disorder have been found to be 1.5 to 8 times more likely in adults with ADHD than in those without, and associated problems of frequent job changes, unemployment, and criminal arrests were found to be more common in this population, as well.4,9 Studies of driving behavior also indicate that adults with ADHD incur higher rates of accidents on the highway and motor vehicle–associated injuries.10 The fact that ADHD is likely to occur with other psychiatric disorders adds to the clinical complexity of both diagnosing and treating the disorder and amplifies the potential for adverse life outcomes.
Comprehensive pharmacoeconomic data are lacking on ADHD's impact in adulthood, but indirect indicators such as the increased rates of criminal involvement, substance abuse, and psychiatric comorbidities along with driving data would suggest that ADHD is a costly disorder. Numerous studies have documented the high societal costs of depression, anxiety, and substance use disorders but have ignored the impact of comorbid ADHD.11–13
Given that ADHD is, by definition, a childhood-onset disorder, it would be useful if a study was undertaken to help us understand the impact of early diagnosis and treatment of the disorder on the development of subsequent comorbid conditions, as well as on the associated costs of treating these secondary conditions as they develop later in life. Whatever the age of clinical presentation, individuals with ADHD may have coexisting conditions that complicate diagnosis and treatment, add to the costs, and compound the impairments associated with the disorder.