In the past 15 years, there has been an increasing awareness of the syndromal persistence of attention-deficit/ hyperactivity disorder (ADHD) into adulthood. Once considered only a childhood disorder, ADHD has become increasingly recognized as a valid psychiatric disorder in adults.1-3 Proponents of ADHD as a valid adult diagnosis do not suggest that ADHD arises de novo in adulthood. Rather, adult ADHD is considered the natural continuation of childhood ADHD, albeit with a different topographical expression of symptoms. The focus of this article is to discuss what is known about ADHD in adults, with a particular emphasis on diagnosis and treatment strategies.
Comparisons with Pediatric ADHD
Prevalence and symptoms. In children, the prevalence of ADHD is typically cited as between 3% and 5% of the general population while in adults, studies suggest that the prevalence is about 4%.4,5 This is not surprising given that longitudinal research indicates that the majority (50% to 70%) of children with ADHD continue to show impairing symptoms as they age.6
ADHD research in children and adults indicates that inattention and hyperactivity/impulsivity are the defining features of the disorder. For example, in a family study of ADHD, more than two-thirds of nonreferred adult relatives of children with ADHD reported current ADHD symptoms at levels comparable to those in pediatric participants with ADHD.7 These data suggest that inattentive and hyperactive/impulsive symptoms are the defining features of ADHD in both clinically referred and nonreferred adults.8-13
Despite the similar symptoms, several core ADHD symptoms described in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) (eg, hyperactivity) lessen or mollify over time.14 For example, Eaton and colleagues15 demonstrated that psychomotor activity levels decline after age 9 in the general population. Thus, "running about or climbing on things inappropriately" may have less predictive power as a diagnostic symptom in adulthood. This has led to some diagnostic confusion and possibly underdiagnosis of adult ADHD.3
In addition, teachers and school personnel are attuned to ADHD and are familiar with the disorder in children, while employers are likely to be less mindful of possible ADHD symptoms in adults. In the absence of a formal screening mechanism, adults with ADHD may also be less likely to be referred for treatment. Although the symptoms appear to be equally defining in children and adults, the topography of these symptoms may be quite different in adults, possibly contributing to ADHD underdiagnosis in adults.16
Comorbidity. Pediatric ADHD commonly co-occurs with multiple psychiatric disorders including mood, anxiety, and disruptive behavioral disorders.17,18 Likewise, adult ADHD is associated with comorbid mood, anxiety, and substance use disorder diagnoses.8,13,19-23 Comorbidity rates in adult ADHD do not differ as a function of gender; this is in contrast to the higher prevalence of externalizing disorder comorbidities observed in boys with ADHD.24,25 ADHD in adults is not always comorbid with other psychiatric conditions, however, and some data suggest that uncomplicated ADHD exists in about 20% to 25% of adults with ADHD.8
Genetics. ADHD is a highly heritable condition (average heritability index, 0.76).26 Family studies of pediatric ADHD suggest that the parents of children with ADHD are more likely than parents of other children to have ADHD themselves.27 The same holds true in adult ADHD; offspring of parents with ADHD are more likely to have ADHD themselves. 28,29 Biederman and colleagues29 found a 57% prevalence of ADHD in children of adults with the disorder, which is much higher than the 15% prevalence of ADHD among siblings of children with ADHD. Genetic factors appear to play a stronger role in those who continue to demonstrate clinically significant ADHD into adulthood than in those whose symptoms are in remission. 30,31 For example, a prospective ADHD study with a 4-year follow-up examined 140 boys with ADHD and 120 boys without ADHD at baseline. By midadolescence, 85% of the boys with ADHD continued to have the disorder. The prevalence of ADHD was significantly higher among the relatives of children with persistent ADHD than among relatives of children with ADHD whose symptoms were in remission.32
Parents of persistent ADHD probands were 20 times more likely to have ADHD than parents of controls, whereas parents of nonpersistent ADHD probands showed only a 5- fold increased risk. Similarly, siblings of persistent ADHD probands were 17 times more likely to have ADHD than siblings of controls, while siblings of nonpersistent ADHD probands showed only a 4-fold increased risk.33 When ADHD persists into adulthood, it is decidedly familial.
Significant functional impairment in educational, marital, interpersonal, and occupational realms and in motor vehicle operation is common in adult ADHD.13,34-40 In fact, recently published longitudinal research findings indicate that ADHD in adults is a far more impairing disorder than many other disorders (eg, anxiety and mood disorders) across multiple domains of major life activities, especially educational and occupational functioning, money management, and management of daily responsibilities.23
Adults with ADHD are also more likely to receive speeding violations and have their driver’s license suspended.13,41 These motor vehicle– related infractions are not related to deficits in driving skills or knowledge. 13 Computer-simulated driving tests also demonstrate that adults with ADHD have more accidents and near-accidents.13
Similar functional impairment findings have been seen in other studies that compared adults with ADHD and psychiatric controls.8,13,24 Morrison20 compared adults who had ADHD with age- and sex-matched psychiatric controls on educational and occupational achievement variables and found that adults with ADHD had fewer years of education and lower rates of professional employment. There is evidence that the lower rates of professional employment are not accounted for by comorbid psychopathology.42
It is not surprising that adults with ADHD have lower rates of professional employment, given that academic underachievement and learning disabilities are common in children with ADHD.37,38 A community study showed that the profile of impairments of adults with ADHD diagnosed in the community was similar to that seen in samples in whom ADHD was diagnosed in academic centers.39 Likewise, data from adults with previously undiagnosed ADHD indicated more psychiatric comorbidity and functional impairments than did controls without ADHD; even when unrecognized, ADHD in adults is functionally impairing.4
Elevated prevalence of substance abuse/dependence has consistently been reported in adults with ADHD.41,43,44 An estimated 17% to 45% of adults with ADHD have histories of alcohol(Drug information on alcohol) abuse or dependence and 9% to 30% have histories of drug abuse or dependence.44,45 A study of treatmentnaive adults with ADHD found that the risk of substance abuse/dependence developing over the life span is 2-fold compared with adults who do not have ADHD (52% vs 27%, respectively). Although a history of conduct or bipolar disorders increases that risk, ADHD is an independent risk factor for later substance abuse/dependence. 35,45-47 Studies have shown that compared with adults who do not have ADHD, adults with comorbid ADHD and substance abuse/dependence have an earlier onset and a greater severity of substance abuse.36,48,49
Likewise, findings indicate that ADHD is more prevalent among substance users.47,50,51 Studies of substance- dependent populations report the prevalence of ADHD ranges from 15% to 25%.42 The presence of ADHD appears to potentiate the substance abuse/dependence, resulting in a more severe disorder and poorer outcomes. 42,52 The increased prevalence of substance abuse/dependence in ADHD has been reported in longitudinal studies that followed children with well-characterized ADHD into adulthood, as well as persons with ADHD that is diagnosed in adulthood. 10,22,46,53 Finally, among those with substance abuse disorder, adults with ADHD have higher rates of separation and divorce and lower occupational achievement than their peers.42
Diagnosing Adult ADHD
DSM-IV criteria for ADHD symptoms are based on earlier DSM editions, expert clinical opinion, and a field trial of the psychometric properties and utility of the item pool.24 The proposed DSM-IV ADHD items were field-tested using a sample of 380 clinically referred children aged 4 to 17 years. The 18 items that appear in DSM-IV correlate highly with parent and teacher ratings of impairment and best differentiate ADHD from non-ADHD disorders.24
Adults were not included in the ADHD field trials for DSM-IV. Thus, there was no attempt to assess the developmental appropriateness of the ADHD symptoms for diagnosing the disorder in adults. For example, DSM-IV symptoms such as “runs and climbs excessively” are clearly inappropriate for adults. Similarly, the cutoff score of 6 of 9 symptoms was based on pediatric data, which may be too restrictive for adults.24,54 Unlike diagnosing ADHD in children, diagnosing ADHD in adults relies highly on self-report. Asking a 42- year-old man to recall behaviors before age 7 most likely introduces recall biases.55 For this and other reasons, the age of onset should be redefined as early adolescence.41,56
In addition to DSM-based checklists, the Wender Utah Rating Scale (WURS) is also used in the diagnosis of adult ADHD.57 A self-report instrument, the WURS was designed to aid in the retrospective assessment of ADHD but was not intended for diagnosis of childhood ADHD in the absence of other clinical information. The WURS is often applied to diagnosing ADHD by the Utah criteria, which include 7 symptom clusters that characterize adult ADHD58:
•Irritability and hot temper.
•Impaired stress tolerance.
To meet diagnostic criteria for ADHD in adults, the Utah criteria require a retrospective childhood diagnosis, ongoing difficulties with inattentiveness and hyperactivity, and at least 2 of the remaining 5 symptoms. Some have argued that the Utah criteria are not specific enough for ADHD and may capture psychiatric comorbidities such as depression.59
The 40-item Brown Attention- Deficit Disorder Scale for Adults,60 which is used to assess symptoms beyond the DSM-IV 9-item inattention symptom list, may be the best tool for clinical diagnosis of adult ADHD.60,61 This scale measures 5 clusters (hyperactivity and impulsivity are not assessed on this scale):
•Organizing and activating to work.
•Sustaining attention and concentration.
•Sustaining energy and effort.
•Managing affective interference.
•Using working memory and accessing recall.
The Conners’ Adult Attention- Deficit/Hyperactivity Disorder Rating Scale—Screening Version62 is a self- and other-report measure of ADHD symptom severity during the past week. The instrument has 30 items that contribute to 3 subscales: inattention (9 items); hyperactivity/ impulsivity (9 items); and ADHD index (12 items).
The World Health Organization Adult ADHD Self-Report Scale63 is another screening tool. The scale includes 18 items generated from symptoms of ADHD typically expressed by adults with ADHD. The 18 items are then mapped onto each of the 18 DSM-IV Criterion A symptoms. Six of these items—4 inattention and 2 hyperactivity/impulsivity— were found to be the most predictive of adult ADHD; the items are listed in the Box.63