Under Diagnosis of Adult ADHD

The Adolescent to Adult Transition

ADHD in children is characterized by developmentally inappropriate and impairing levels of hyperactive, impulsive, and/or inattentive symptoms (American Psychiatric Association [APA], 2000). During adolescence, changes in the environmental context, expectations, and maturational processes result in a different range of clinical presentations and impairments to those seen in children (Wolraich et al., 2005). Although all symptoms of ADHD can persist, hyperactivity tends to be less visible during the adolescent years, whereas problems related to inattention, such as academic or work performance and structuring of daily routines that may have been less noticeable in childhood, can become more obvious and problematic. This is particularly true because problems with inattention tend to persist with age, and demands on individuals become more complex as people grow older.

In some cases where the symptoms of ADHD during childhood are of the predominantly inattentive type and particularly in children with no comorbid disruptive behavioral disorders, the diagnosis is more likely to go unrecognized. For example, Milich, Balentine, and Lynam (2001) found that among children with the inattentive type, referral and diagnosis of ADHD occurs at an older age compared with those with the combined type. Yet high levels of social impairment, chronic low self-esteem, and anxiety may emerge during adolescence, in addition to impairments related to difficulties with sustaining attention, aspects of self-organization, and inner restlessness. These problems can become even more apparent among young adults as the demands for independence and higher levels of social function increase and problems with peer relationships become more obvious as the social environment changes.

ADHD in adults remains a diagnosis that often goes unrecognized (McCarthy et al., 2009). As such, unidentified ADHD in childhood is likely to remain unidentified in adulthood (Biederman, Faraone, Spencer, & Wilens, 1993; Weiss & Murray, 2003). Although some progress has been made in recent years, it is still clear that this remains a considerable problem, even for adults with typical presentations of ADHD (Kooij et al., 2010). For high-functioning individuals with ADHD, this can be a particular problem as circumstances such as obtaining good school grades and the development of effective coping strategies that ease the psychosocial and functional burdens of ADHD can result in failure to recognize the condition, even where there are symptoms of impaired mental health related directly to the persistence of ADHD. Impairment can also emerge later in life as the greater complexity of daily tasks coupled with a decline in family support structures may make previously hidden impairments more prominent and in some cases disabling (Able, Johnston, Adler, & Swindle, 2007; Ramsay, 2007; Weiss & Weiss, 2004). Furthermore, symptoms of ADHD may be reflected in more subjective states such as irritability, impatience, difficulty sleeping due to physical and mental restlessness, tiredness or distress, and the use of drugs or alcohol to relieve symptoms.

In contrast, for those individuals who faced ADHD-related impairments during childhood, they may find that adulthood gives them greater freedom to tailor their environment to remedy the difficulties they experienced when they were younger. Weiss and Weiss (2004) provided the example of a child who feels restless sitting in class, growing up to become a real estate agent whose job involves frequently moving from location to location. However, the authors warn that while such individuals may adapt their occupational environments to mask impairments, they frequently experience impairments in quality of life, social relationships, driving ability, and other functional and psychopathological impairments.

Challenges With Diagnostic Criteria

The fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA, 1994) was the first among the editions to recognize that the symptoms of ADHD can persist into adulthood, thus clarifying the persistent nature of the disorder in at least a subset of cases (Clarke, Heussler, & Kohn, 2005; Moss, Nair, Vallarino, & Wang, 2007). Under DSM-IV, there are five criteria that must be met in order for an individual to be diagnosed with ADHD (APA, 2000). The first criterion is the presence of six or more out of nine symptoms of inattention and/or hyperactivity/impulsivity. Second, the symptoms must be present in a minimum of two different settings, for example, at home and at college or work. Third, some of the symptoms with impairment must have begun in childhood before the age of 7. Fourth, evidence is required of “clinically significant” impairment in social, academic, or occupational functioning. Finally, the symptoms must be pervasive and not confined to random periods of recurrence and extinction, as this is the hallmark of episodic disorders such as depression or bipolar disorder (Asherson, 2005; Clarke et al., 2005; Feifel & MacDonald, 2008).

Although the DSM-IV is commonly used for the diagnosis of ADHD in adults, numerous issues have been identified with these criteria that can lead to under diagnosis and misdiagnosis. McGough and Barkley (2004) explaine that the current criteria have not been validated in adults, do not include symptoms and diagnostic thresholds that have been age adjusted to take into account developmental changes that occur in ADHD, and fail to identify all adults who are significantly impaired by ADHD symptoms. For example, symptoms such as procrastination, time management problems, overreacting to frustration and mood instability, low boredom threshold, and sleep problems are common complaints of adults with ADHD that are not included in the current symptom list (Asherson, 2005; Davidson, 2008).

Although the number of ADHD symptoms as defined in the DSM-IV may decline with age, so that not all adults with persistence of ADHD symptoms from childhood meet the full diagnostic criteria, they may still experience significant impairments (Mick, Faraone, Biederman, & Spencer, 2004). The numerous studies that show a decrease in ADHD symptoms with age may show a true remission of the symptoms, but the decrease may also be an indication of inappropriate measurement of symptoms in adults (Davidson, 2008) and/or the development of coping strategies. The impression of a largely improving condition could also come about because most studies do not include more objective measures of ADHD symptoms or a comparison control sample. When this was done in an epidemiological 10-year follow-up sample of children from the age of 7 to 8 through 16 to 18 years, it was found that while objective measures of ADHD symptoms declined with age, this occurred for both case and control samples, and differences between the two groups were retained in the older age group and were associated with a range of clinical and psychosocial impairments (Taylor, Chadwick, Heptinstall, & Danckaerts, 1996). Simply recycling descriptions of childhood symptoms and applying the same thresholds for the presence of symptoms in adults will result in increased difficulty in the appropriate detection of impairing levels of ADHD as individuals with ADHD grow older (Davidson, 2008; Faraone et al., 2000).

Related to this, the type of impairment caused by ADHD symptoms in adults may be different from that seen in children (Davidson, 2008). There has been a debate as to whether the minimum of six criteria for children results in under diagnosis when applied to adults (Moss et al., 2007). Smith and Johnson (1998), using Rasch analysis, found that four DSM-IV items, including “difficulty waiting in lines” and “interrupting or intruding on others,” were the most sensitive in detecting ADHD in adults. Furthermore, these differed from the six items most sensitive in children, such as “fidgets or squirms in seat” and “difficulty remaining seated.” Murphy and Barkley (1996) found that the cutoff of six of nine hyperactive-impulsive symptoms and six of nine inattentive symptoms required in the DSM-IV was statistically extreme as it fell 2.5 to 3.0 standard deviations above the mean (i.e., 99th percentile) for ratings of current ADHD behavior whereas in children, a 1.5 standard deviation difference (93rd percentile) is used to establish deviation from the norm. In this same study, results showed that a cutoff of four of nine inattentive symptoms and five of nine hyperactive symptoms was sufficient to identify adults (aged 17-29) using the traditional 1.5 standard deviation difference. Kooij and colleagues (2005) also found four symptoms, as opposed to the established threshold of six symptoms, appropriate for making a current diagnosis of ADHD in adults. The main point here is that these studies indicate that four symptoms rather than six symptoms seem a more appropriate threshold for the current symptoms in adults because they still indicate significant impairment in many cases. For these reasons, the revised DSM-V criteria are expected to adopt this change in threshold for adults (www.dsm5.org).

There are discussions among experts regarding what constitutes functional impairment, especially in cases where the impairment may not appear to be extreme. This is critical to one of the key requirements for the diagnosis of ADHD, that the symptoms should be associated with significant clinical or psychosocial impairments. There can, for example, be disagreement regarding diagnosis of ADHD in adults who perform well at work but expend excessive amounts of time and energy to overcome ADHD symptoms, leading repeatedly to episodes of being burnt out (Wasserstein, 2005). However, while a few adults with ADHD may function well at work, they may also describe considerable distress due to the degree of effort required to control symptoms of ADHD and the experience of internalizing symptoms related to ADHD such as constant distractible thought processes, low self-esteem, and mood instability (Asherson, 2005; Skirrow, McLoughlin, Kuntsi, & Asherson, 2009). Further difficulties may arise in the retention or development of close personal relationships. It has also been argued that some adults with ADHD with a high IQ may not experience deficits in function that are sufficient to warrant disability provisions provided in some countries, such as the mandated extra standardized testing time per the Americans Disabilities Act for those with ADHD (Antshel et al., 2009). However, high function in the workplace does not always mean that those individuals are not struggling to cope with their symptoms. Performance may still be impaired compared with an equivalent age and IQ-matched group and/or they may have a markedly reduced quality of life as a result of more subjective aspects of the disorder effecting effort, mood, and the ability to relax, sleep, and so on.

Another question that often arises is the appropriate age of onset to establish the diagnosis of ADHD. The DSM-IV requirement for early childhood onset of symptoms, before the age of 7 years can be especially problematic as the diagnosis is based on recall which can be inaccurate, especially if the adult no longer has access to any caregivers or older siblings who may provide a more accurate account of early childhood problems (Dias et al., 2008). When evaluating ADHD in children, it is usual that ADHD symptoms are reported by a parent or other informant such as teachers. For adults, it can be extremely challenging to recall the time course and nature of symptoms as well as impairments related to them (Dias et al., 2008). This means that in clinical practice, adults presenting with ADHD often cannot properly recall childhood symptomatology, and independent evidence of the disorder such as school reports are not always available. Furthermore, the age of onset of 7 years has been shown to have no specific predictive value, with similar course and outcomes for those with a later age of onset (Applegate et al., 1997; Bell, 2010). As a result, the revised DSM-V edition of the ADHD criteria are expected to change the age of onset criteria to some symptoms present before the age of 12 years (www.dsm5.org), including allowance for impairment from the symptoms to emerge later in adult life.

Further problems may arise if the more restricted International Classification of Diseases 10 (ICD-10) criteria for hyperkinetic disorders (HKDs) are applied, which in effect describe a severe subtype of the DSM-IV combined subtype diagnosis. While there are limited follow-up data using HKD, it is likely that many impaired adults with ADHD would not meet these restricted criteria. In childhood, the diagnosis of HKD has been used in U.K. guidelines to indicate that treatment with medication is required immediately, whereas those with broader criteria might in some cases delay treatment with medication while psychosocial interventions are implemented first (National Institute for Health and Clinical Excellence [NICE], 2008). However, no such discussion was included in the NICE guidelines for adults with ADHD because there was a lack of data to address this point. It is however expected that, as in childhood, adults who meet HKD criteria would be severe cases where incorrect diagnosis and delay in pharmacological treatment would be highly detrimental to the individual concerned. The particular difficulty in applying the HKD criteria to adults is that the definition has not been adapted for adults and although it lists similar symptoms as those of the DSM-IV, it requires the presence of marked levels of hyperactivity. This can lead to under diagnosis in adults as overt overactivity tends to decline with increasing age (Biederman, Mick, & Faraone, 2000; Larsson, Lichtenstein, & Larsson, 2006). Nevertheless in practice, few clinical services use these criteria for adults with ADHD, even with countries where the ICD criteria are generally applied (Kooij et al., 2010).

Spurred by the current diagnostic disparities that arise when using the current scales in adults, some experts advocate a change from the current criterion-referenced diagnosis in diagnostic scales such as the DSM-IV and ICD-10 to a norm-referenced diagnosis for adults (adopting a dimensional threshold approach) but emphasize that given the clinical implications of such a change, comprehensive empirical research supporting the theory that this change would lead to more accurate diagnoses in adults is necessary (Davidson, 2008).

Self-Reporting

Because diagnosing ADHD in adults relies in part on the ability to recall childhood symptoms, issues in the accuracy of self-report arise, such as differences in symptom recall between an adult’s self-report and a parent’s report. A study by Barkley (2002) found that the persistence of ADHD into adulthood is 5 to 9 times higher when based on parent accounts than when based on a self-report. Parents were also better able to predict functional impairments than were adult’s self-reports. Zucker, Morris, Ingram, Morris, and Bakeman (2002) also noted that adults with ADHD noted fewer past inattentive symptoms than their parents but that this difference in reporting did not exist for past hyperactivity symptoms. These findings suggest that in at least a proportion of cases, the use of using self-report will underestimate the persistence of the disorder into adulthood (Barkley, 2002; Dias et al., 2008).

Patient rating scales, such as the Brown Attention Deficit Disorder Scale (BADDS) and Conners’ Adult ADHD Rating Scale (CAARS) are sometimes employed to aid in diagnosis and are especially useful for clinicians less experienced in the formal diagnosis of adult ADHD (Clarke et al., 2005). The use of rating scales can however be problematic because they lack validation in individual cases, and they should only be used to complement a comprehensive diagnostic assessment including a clinical interview that reviews the developmental history and the development and course of the specific symptoms and impairments of ADHD. Rating scales however have particular value in screening for and monitoring of symptoms and impairments during any course of treatment and follow-up assessments (Mehringer et al., 2002). In terms of validity, a comparison of CAARS and BADDS administered with a structured clinical diagnostic interview demonstrated a missed diagnosis rate of 39% for the CAARS and 16% for BADDS (Kooij et al., 2008). Furthermore, there is a false positive rate so that screening positive for ADHD on a scale should always be followed by a full diagnostic assessment to confirm the diagnosis and clarify the impairments involved. The Wender Utah Criteria is credited for taking into account developmental changes in the symptom expression of adults compared with children with ADHD. However, it is often criticized because it requires the absence of other psychiatric disorders and does not include inattentive symptoms (Moss et al., 2007). Thus, this measure is not successful in identifying adults with primarily inattentive symptoms and fails to identify some adults with co-occurring disorders (McGough & Barkley, 2004). Using reports from several informants is considered to be the best practice given the research showing that adults with ADHD tend to underreport the presence and severity of ADHD symptoms (Asherson, 2005; Davidson, 2008).

Given the potential difficulties with establishing the clinical diagnosis in adults using the current DSM-IV criteria, and until diagnostic criteria validated specifically for adults are available, McGough and Barkley (2004) recommended that clinicians should be flexible in the way that they apply the current operational criteria when identifying ADHD in adults. More specifically, they suggest a change in the criteria for the onset of symptoms and impairment from before the age of 7 years to before the onset of puberty, consider diagnosing adults with four rather than six current hyperactive-impulsive and/or inattentive symptoms when these are seen as the persistence of impairments related to ADHD symptoms that started in childhood or adolescence, and seek to corroborate patient reports with reports from other individuals whenever feasible. These changes in criteria are expected to be adopted in DSM-V (www.dsm5.org), are recommended by NICE (2008), and are widely adopted by specialists in the diagnosis and treatment of ADHD in adults (Kooij et al., 2010). These adaptations have also been incorporated in the new semistructured Diagnostic Interview for ADHD in adults (DIVA 2.0) that is currently being translated in many languages (available for free at www.divacenter.eu).

Cultural Influences on Diagnosis and Media Representation

International epidemiological studies offer some insight on the influence of cultural background that appears to play a role in various psychiatric phenomena from the meaning of expressed emotion to linguistic structure and content of delusions (Canino & Alegría, 2008). There is however limited research on the role of cultural differences in ADHD recognition and diagnosis.

A systematic review of 102 worldwide population-based studies of ADHD showed significant differences in the reported worldwide prevalence of ADHD but found that these differences could be attributed to methodological differences, particularly the operationalization of the diagnostic criteria used and the evaluation of impairment, suggesting that cultural context contributes to variability in the estimated prevalence rates (Polanczyk, De Lima, Horta, Biederman, & Rohde, 2007). The European Commission Employment and Social Affairs Directorate General published a report that explored trends in ADHD in adults across six European countries and concluded that country-specific differences can lead to different conceptualizations of ADHD. The report ends with a call for further research, citing that a pan-European research project is needed which will add to the existing knowledge about ADHD and legitimize the disorder in adults (ADHD Europe, 2002).

The perception of ADHD in the nonscientific print media remains a relatively controversial one. Schmitz, Filippone, and Edelman (2003) completed the only published systematic content analysis of print media for social representations of ADHD. The review was limited to U.S. print media publications between 1988 and 1997 and focused on representations of ADHD in children and adults. They examined how the various representations of ADHD influence perceptions among individuals experiencing ADHD symptoms and how this may in turn affect subsequent mental health treatment decisions. The findings showed the evolution of proposed causes of ADHD represented in the print media, shifting from unknown in the late 1980s to neurobiological and genetic explanations in the early to mid-1990s, with decreased emphasis on environmental factors such as parenting skills and diet. The authors found, however, that despite the emergence of a biological and genetic discourse in relation to ADHD, discussions of the use of medication in the media remained ambiguous in the same period, as evidenced by statements such as calling drugs a “quick fix” or a “chemical cosh.”

Conrad and Potter (2000) performed a more general but nonsystematic exploration of adult ADHD in the public sphere, including the review of articles in various publications from 1975 to 1999 that focused on ADHD. They found a significant increase in articles in both the professional and lay media over this time span with the presentation of adults with ADHD starting from 1993 onward and corresponding to an increase in the numbers being diagnosed with ADHD in adulthood. Racial and gender discrepancies in the representation of ADHD were also highlighted as the images presented in the media were primarily of White, middle-class, preadolescent boys perhaps implying that women, ethnic minorities, and adults are less likely to be affected by the disorder.

There are still significant gaps and misconceptions in the lay and professional understanding of ADHD in adults. A survey by McLeod, Fettes, Jensen, Pescosolido, and Martin (2007) found a general lack of knowledge within the U.S. public about ADHD, especially among men, non-White minority groups, and older Americans. As this study was assessing childhood ADHD and was conducted in the United States, it seems likely that even less would be known about ADHD in adults when surveying public opinion in countries where diagnostic prevalence rates for ADHD in adults are much lower, such as many parts of Europe (Kooij et al., 2010). Furthermore, in some cases, the general understanding of ADHD may be based on unsubstantiated information, which may then hinder proper education and the provision of effective treatments and support. For example, in Germany, where there is a widely held belief that ADHD is caused predominantly by nutritional deficiencies/food allergies and thus can be treated primarily with dietary modification, people may have very different ideas about the disorders than in other countries where this view is less prevalent (Schmidt et al., 1997).

The overall presentation of ADHD in the media was criticized, in the “International Consensus Statement on ADHD,” as irresponsible in its depiction of ADHD as a dubious and unsubstantiated diagnosis (Barkley, 2002). These questions about the presentation of ADHD are significant given the potential for media representations of ADHD to influence the health decision of individuals experiencing ADHD symptoms. Social psychology research has shown that the sharing of social representations in a social group can influence the identity that its group members assume (Hermans, 2003; Oyserman & Markus, 1998; Schmitz et al., 2003; Wagner et al., 1999).

Social representation of a disease or disorder is critical in overall recognition particularly with disorders like anxiety, depression, and ADHD that may be best perceived as extremes of dimensions of normal behavior, and defined as categorical disorders when symptoms are extreme and give rise to clinically meaningful impairments (Chen et al., 2008; NICE, 2008). Gervais and Jovchelovitch (1998) discussed the relationship between health and identity and that professional opinion is not the only source of knowledge that guides individuals in making health decisions. Lay knowledge must also be examined to provide the full spectrum of how an individual understands his or her symptoms and approaches to treatment. As Gervais and Jovchelovitch explained, it is through the lens of culture and traditional knowledge that we think, feel, and understand our environment. Indeed, making sense of adult ADHD proves a challenging task for patients and physicians, as there is still debate in some circles as to whether ADHD even exists as a medical disorder or is simply a “cultural construct” (Asherson et al., 2010; Moncrieff & Timimi, 2010; Timimi & Taylor, 2004).

Waite and Ivey (2009) commented that as the research guidelines that are currently used in the assessment and diagnosis of ADHD have traditionally focused on White Caucasian males, women and those from minority backgrounds may be falling through “diagnostic cracks.” Demographic characteristics driving disparities in diagnosis of ADHD are age, race/ethnicity, and gender. There is a clear bias toward under diagnosis in minorities: Specifically, U.S. studies have found African American boys more likely to be rated higher on antisocial traits, and a U.K. study described a “mad/bad” paradox where White children with ADHD symptoms are classified as having a clinical disorder, whereas Black children exhibiting the same symptoms are simply labeled as “bad” (Epstein, March, Corners, & Jackson, 1998; Evans, 2004). Findings that raters are more likely to rate minority children exhibiting hyperactivity as “deviant” may generalize to adult populations as well, although there is very limited data on this point and further research is needed (Sonuga-Barke, Kuldeep, Taylor, & Sandber, 1993).

With respect to gender, Simon, Czobor, Balint, Meszaros, and Bitter (2009), in a meta-analysis of demographic correlates with ADHD in adults, reported gender proportions that were “neither balanced nor representative of the target population,” generally with a higher prevalence in males than females, although the gender differences were less pronounced in adults than in children. They provide possible reasons for the more balanced gender distribution of ADHD in adults including the fact that while children are often referred by parents or teachers for exhibiting overtly disruptive behaviors, which tend to be more prevalent in boys (Levy, Hay, Bennett, & McStephen, 2005), adults are often referred because they are having difficulties in managing activities of daily life or comorbid disorders such as anxiety, which is more common in females. Furthermore, in general, women are more likely to seek help for mental health problems than are men. Most studies find higher rates of adult women with ADHD than in child clinics, sometimes even outnumbering the men in certain populations (Almeida Montes, Hernandez Garcia, & Ricardo-Garcell, 2007; DuPaul et al., 2001; Kooij et al., 2005). Overall these observations demonstrate the importance of cultural factors and expectations that influence perceptions of the disorder as well as the different courses of the disorder between the genders and the impact on referral rates at different developmental stages.

Health System Impacts on Diagnosis

Country-specific variables contributing to differences in diagnosis are not limited to culturally influenced representations of the disorder but can also include actual differences in health care systems. As Conrad and Potter (2000) commented, “managed care affects all aspects of medicine, including psychiatry” (p. 572). While referring only to U.S. managed care, this statement can be generalized to emphasize that whatever the particular health care structure is in a given country, it can potentially influence quality of care and availability of treatments. Countries with different health systems likely have disparities in the level of severity of the “typical” patients they see, which can influence country-specific findings. In the U.S. system where medical insurance is usually required before treatments can be provided, some of the most severe cases of ADHD may be unable to access diagnostic and treatment services and those receiving treatment may be overrepresented by relatively high-functioning individuals with ADHD. In contrast, in open health care systems such as the U.K. National Health Service, referrals for ADHD are likely to include a broader range of patients, including a larger proportion of the most impaired. This may give rise to different perceptions and thresholds for symptoms and impairments required to establish the diagnosis in different regions of the world.

While no studies assessing the relationship between health care delivery model, diagnosis, and subsequent treatment of adults with ADHD across countries were identified in the literature, J. Stevens, Harman, and Kelleher (2004) examined diagnosis and stimulant treatment among children varying in race and insurance type in the United States for the years 1995 to 2000. The study found significantly lower numbers of Hispanic American youths being diagnosed and treated for ADHD and significantly higher numbers of youths on Medicaid being diagnosed compared with other types of insurance. A retrospective study reviewing the same data estimated that U.S. physician visits for adults with ADHD increased in the early 2000s with psychiatric comorbidity and reimbursement source being significant in predicting ADHD treatment utilization (Sankaranarayanan, Puumala, & Kratochvil, 2006).

Furthermore, primary care physicians (PCPs) in the United States have different views on the diagnosis of ADHD in adults. Clearly, diagnosing patients correctly is crucial, as misdiagnosis of ADHD leads to inappropriate and ineffective interventions by psychiatrists and mental health providers (Asherson, Chen, Craddock, & Taylor, 2007). In a study by Adler, Shaw, Sitt, Maya, and Morrill (2009), 400 PCPs who managed patients with ADHD and various other mental health conditions completed a survey assessing their experiences and attitudes on diagnosis and treatment of various mental health conditions. Results indicated that 48% of PCPs felt uncomfortable diagnosing ADHD in adults. Furthermore, 44% reported the view that no clear diagnostic criteria exist for ADHD in adults. A total of 85% reported that they would be more comfortable diagnosing and treating ADHD in adults with the aid of better validated screening tools and different pharmacotherapy options. Thus, the results indicated that the issue is not entirely related to lack of knowledge about ADHD in adults but a lack of centrally accepted diagnostic and treatment guidelines and awareness of available screening tools. Still, even with uniform diagnostic criteria, the impact of culture can still skew diagnostic prevalence. As Mann et al. (1992) found in a study including clinicians from the United States, Japan, China, and Indonesia, even if provided with uniform diagnostic criteria, professionals from different backgrounds differ in their perceptions of hyperactivity and give markedly different scores to individuals displaying comparable levels of hyperactive behaviors.

Burden of ADHD in Adults

ADHD in adults can result in impairments in many areas of daily life and may pose a significant societal burden such as adverse effects on interpersonal and family relationships and increased accidents and rates of criminal behavior. It is associated with an increased risk of other psychopathological conditions (Figure 1 [developed by the authors]; Able et al., 2007; Riccio et al., 2005). This section discusses the increased risk of psychopathological conditions, psychosocial burden and decreased productivity, impact on driving, increased criminality, and comparisons between diagnosed and undiagnosed adults with ADHD.

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Figure 1.

Psychosocial burden of adult ADHD

Increased Risk of Psychopathological Conditions

There is mounting evidence that young adults with ADHD are at high risk for a range of adverse psychiatric outcomes. Biederman and colleagues (2006) conducted a case-control 10-year prospective study of young adults with ADHD and found that, by a mean age of 21, the young adults had markedly elevated lifetime prevalence of major psychopathology (mood disorders and psychosis), anxiety disorders, antisocial disorders, developmental disorders (language impairments and tics), and substance dependence disorders. Specifically, the respective hazard ratios for the prevalence of these conditions were 6.1, 2.2, 5.9, 2.5, and 2.0 (p < .05) among young adults with ADHD relative to controls. Furthermore, their data indicated that not only is ADHD associated with an increased risk of developing co-occurring mental health disorders, but it may also affect the clinical course of such conditions; for example, giving rise to increased rates of affective disorder episodes in patients with ADHD and a mood disorder, compared with those with mood disorders in the absence of co-occurring ADHD (Ryden et al., 2009).

In longitudinal studies, the onset of ADHD precedes substance use disorders. Furthermore, the early age of onset of ADHD precludes a causal role of substance abuse on ADHD in nearly all cases, indicating that ADHD is not secondary to substance use disorders in most patients (Bukstein, 2008). Furthermore, although individuals with ADHD are at increased risk for substance dependence, a prospective study found that early treatment of ADHD reduced the risk of developing a substance use disorder (Mannuzza et al., 2008). In this study, 176 Caucasian male children (ages 6-12) with ADHD who were treated with methylphenidate (MPH) were followed up at late adolescence and compared with a group of 178 non-ADHD controls. The findings showed a significant positive relationship between age at treatment initiation and the development of nonalcohol substance use disorder. These findings have not however been replicated in all other data sets, and the overall conclusion from meta-analysis of comparable data sets is that there is no increased risk of developing a substance use disorder following treatment for ADHD, and treatment may lead to reductions in later substance abuse (Mannuzza et al., 2008; Wilens, Faraone, Biederman, & Gunawardene, 2003).

The increased risk of addiction in people with ADHD may not be limited to alcohol or drugs. For example, a recent cross-sectional study that used the Chen Internet Addiction Scale and Adult ADHD Self-Report Scale (ASRS) to assess 2,793 students across eight colleges in Taiwan found that Internet addiction was associated with attention deficit (odds ratio [OR] = 1.40; 95% confidence interval [CI] = [1.30, 1.52]) and impulsivity (OR = 1.32; 95% CI = [1.16, 1.51]; Yen, Yen, Chen, Tang, & Ko, 2009). The researchers found that the association was more significant in females than males and they suggested that because depression has been reported to be associated with internet addiction, high comorbidity of depression among women with ADHD might result in higher rates of Internet addiction.

ADHD also appears to increase the risk for the later development of conduct and psychopathological problems. An epidemiological study by Taylor et al. (1996) followed up a group of untreated children with hyperactivity and conduct problems from ages 7 to 8 through 16 to 18. Here the term hyperactivity refers to criteria that are close to ICD-10 HKD. They found that hyperactivity predicted later psychopathological problems even after accounting for co-occurring conduct problems. The consequences of untreated hyperactivity in this study included an increased risk for psychiatric diagnoses, persisting hyperactivity, violence and other antisocial behaviors, and social and peer problems. Further unpublished follow-up data at age 27 years showed that maintenance of co-occurring problems such as symptoms of depression and affective lability was predicted by current levels of ADHD symptoms rather than the previous diagnosis in childhood (Stringaris, Hawkins, McLoughlin, Quereta, Asherson, Sandberg, & Taylor, in press).

Psychosocial Burden and Reduced Productivity

Qualitative interviews with adults with ADHD can provide an in-depth understanding of the impacts of this disorder from the patient perspective. Brod, Perwien, Adler, Spencer, and Johnston (2005) examined manifestations of ADHD in adults through interviews with patients. Based on the findings, the researchers identified five areas of life that adults with ADHD felt were most impacted by their disorder: work, daily activities, relationships, psychological well-being, and physical well-being. They found that all of the participants in their study reported impairments in productivity due to poor time management, procrastination, disorganization, problems in follow-through, and distraction. These impairments were present in job-related productivity (e.g., maintaining a job) and in daily living productivity (e.g., paying bills on time). In terms of health, the participants reported feeling anxious and frustrated with the impact of ADHD symptoms which they often related to feelings of low self-esteem. The participants reported that many of these same impairments pose difficulties in personal relationships, leading for example to tension in their relationships. It should be noted that Brod and colleagues also identified positive outcomes that were also reported by the adults with ADHD. Specifically, they reported believing that aspects of their ADHD served to increase their creativity and that this could at times be channeled to promote success in productivity and relationships. Still, these reports were in the minority and the majority of participants reported quality-of-life impairments.

Follow-up studies demonstrate the impairments associated with ADHD. Barkley, Fischer, Smallish, and Fletcher (2006) followed patients with a primary diagnosis of ADHD at the age of 8 years to the age of 25 years. Compared with a control group, the patients at follow-up had significantly more dismissals at work, more relationship crises, a higher number of children, more financial problems, more substance-related disorders, more failures at independent living and returns to parents’ homes, more suicide attempts, more previous convictions, and more inpatient treatments (Barkley et al., 2006).

Biederman and colleagues (2006) examined the impact of ADHD on employment using a telephone survey with two groups of adults: those diagnosed with ADHD (n = 500) and age- and gender-matched controls (n = 501). They found that significantly fewer adults in the ADHD group achieved academic milestones beyond high school compared with the controls, and that only 34% of the participants with ADHD were employed full-time compared with 59% of the controls (p < .001). Also in terms of education, they found that individuals with ADHD reported being less likely to handle a large academic workload, concentrate on their course work, or organize their assignments in the college setting. Barkley, Fischer, Edelbrock, and Smallish (1990) found a threefold increased likelihood of failing a grade or suspension and an eightfold increased likelihood of school expulsion or dropout among adolescents with ADHD compared with those without ADHD.

While children with ADHD are less likely to attend college in the United States (Barkley et al., 1990), there are nevertheless a sizable number of adults with ADHD entering college in recent years (DuPaul et al., 2001; Rabiner, Anastopoulos, Costello, Hoyle, & Swartzwelder, 2008). Rabiner et al. (2008) found, in a study examining college adjustment in students, that in a group of students who reported having ADHD, there were higher rates of concern over academic performance, depressive symptoms, and smoking though the patients on pharmacological treatment for ADHD did not report that treatment improved adjustment. Although there were several limitations to this study, including small sample size and lack of research diagnostic assessments, this study indicates the need to increase the knowledge currently available regarding adjustments necessary for adult students with ADHD.

Economic Burden of ADHD in Adults

The impact of ADHD in adults translates into significant economic burden (Table 1). One limitation of these studies is that currently they are predominantly from the United States and further studies are needed to evaluate the health care and economic burden in other countries.

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Table 1.

Studies Assessing Direct and Indirect Costs of Adult ADHD

Source	Sample	Data	Key findings
Swensen et al., 2004	ADHD patients aged 18 to 64 (N = 444; child sample not included); non-ADHD control matched on age, gender, state of residence, employment status	Administrative medical, pharmaceutical, and disability claims for a Fortune 100 company’s employees	Compared with non-ADHD controls, ADHD had a higher probability of having at least one accident claim than controls (38% vs. 18%) and greater medical costs US$483 vs. US$146 ($US 1998).
Birnbaum et al., 2005	Treated ADHD patients aged 19 to 44 (N = 171) and family members; non-ADHD controls matched on age, gender, employment status, geographical location	Administrative claims and health care data from a single large Fortune 100 company	Total excess cost in year 2000 of treated ADHD patients compared with untreated controls were 3.6 billion and 9.4 billion, respectively ($US 2000). Total excess cost attributable to work loss = US$3.7 billion.
Secnik, Swensen, and Lage, 2005	ADHD patients aged 18 to 64 (N = 2,252) diagnosed between 1991 and 2001 retrospectively identified; non-ADHD control matched on age, gender, type of insurance coverage, and geographical location	Administrative and health care claims data from six Fortune 200 companies	Compared with non-ADHD controls, ADHD adults had significantly higher total medical costs (US$5,651 vs. US$2,771 p < .001; $US 2005). Also, ADHD adults had more lost workdays (4.33 vs. 1.13 days, p < .01).
Kessler, Lane, Stang, and Van Brunt, 2009	All employees in firm (N = 2,656); survey administered to all employees to assess ADHD using ASRS	Survey data from a health risk appraisal survey in a large manufacturing firm	Estimated prevalence of ADHD was 1.9%; ADHD was associated with 4% to 5% reduction in work performance, greater odds of sickness absence, and workplace injuries; human capital value of ADHD-related lost work performance estimated at US$4,336 ($US 2009) per worker.

A 2005 report from the U.S. National Comorbidity Survey Replication estimated that ADHD in adults is associated with more than 120 million workdays lost in the United States annually and placed the human capital value of this loss at US$19.5 billion (Kessler et al., 2005). Kessler, Lane, Stang, and Van Brunt (2009) suggested the cost-effective benefits of workplace ADHD screening given (a) findings that show beneficial effects of treatment on adults with ADHD (Adler et al., 2008; Barkley, Murphy, O’Connell, & Connor, 2005) and (b) that the number of adults with ADHD in treatment is far lower than the actual number of adults with ADHD (Kessler et al., 2006). The negative impact of ADHD on work performance was estimated to be an annual human capital cost of US$4,336 per worker and is higher than the published estimates for most other chronic disorders (Kessler, Greenberg, Mickelson, Meneades, & Wang, 2001; Kessler et al., 2009). Furthermore, this decrease in work performance is especially insidious as the lost productivity is primarily a result of decreased on-the-job performance rather than sickness-provoked absenteeism and thus is more difficult to spot and manage (Kessler et al., 2009).

Kessler et al. (2009) projected that even if treatment only led to a 25% reduction in loss, this financial gain would exceed the cost of treatment. Using health care (medical and prescription drug) and disability and work absence data for a single large U.S. company during the year 2000, Birnbaum and colleagues (2005) estimated the total excess cost of treated and untreated adults with ADHD at US$3.6 billion and US$9.4 billion, respectively. The total excess cost attributable to work loss among adults with ADHD was US$3.7 billion. Cohen and Morley (2009) also suggested that adults with ADHD may face scrutiny and judgment from coworkers and superiors as their inattention may be labeled as laziness or a lack of motivation. Clearly, there is a need to formally evaluate the effectiveness of pharmacological and nonpharmacological treatments on the economic and personal impact of ADHD in the workplace.

ADHD in adults is also associated with increased service costs. For example, medical resource utilization was found to be more than 50% for adults with ADHD compared with controls, not including treatment for ADHD itself (Goodman, 2007). Analysis of medical claims data in the United States from more than 400 adults with ADHD demonstrated that compared with controls, adults with ADHD had a greater probability of having at least one accident claim (38% vs. 18%, p < .05) and significantly higher costs associated with those accidents (Swensen et al., 2004). Secnik, Swensen, and Lage (2005) analyzed claims data for 4,504 employees from six U.S. companies, and they found that those with ADHD had significantly higher outpatient, inpatient, and prescriptions drug costs relative to controls. The total medical costs were US$5,651 for employees with ADHD compared with US$2,771 for the controls (p < .001). In addition, adults with ADHD had more lost workdays relative to the controls (4.3 vs. 1.1 days, p < .01).

Impact on Driving

The core symptoms of ADHD, including inattention, hyperactivity, and impulsivity (and the association of ADHD with problems related to executive functions), are associated with poorer driving performance and greater risk for adverse driving outcomes (Barkley & Cox, 2007). Inattention and distractibility while driving is one of the most common reasons for vehicle crashes in the United States (Lam, 2002; U.S. General Accounting Office, 2003). Drivers themselves report inattention as the single most frequent reason for their vehicle crashes (Barkley, 2002). According to Barkley and Cox (2007), young drivers with ADHD are 2 to 4 times more likely to be involved in a traffic accident, 6 to 8 times more likely to have their license suspended and 3 times as likely to have driving-related injuries. In addition, ADHD is associated with emotional and behavioral problems that can enhance driving risks, including excessive risk taking, poorly controlled anger and aggression, reduced use of seat belts, greater use of alcohol and drugs, and the presence of persistent emotional and behavioral difficulties (Barkley, 2004; Barkley & Cox, 2007).

Meta-analyses of available data confirm the association between ADHD and driving impairments and this has led, for example in the United Kingdom, to ADHD being a disorder that should be declared when applying for a driving license. In a project funded by the European Commission under the Transport Research and Technological Development (RTD) Programme, Vaa (2003) performed a meta-analysis examining the association between disorders, age, and accident involvement. They found that individuals with ADHD had a 54% higher risk of being involved in an accident compared with individuals without ADHD (relative risk = 1.54). In a more recent meta-analysis, Jerome, Segal, and Habinski (2006) found that the mean number of self-reported motor vehicle collisions was significantly higher in five of seven studies and that ADHD individuals committed significantly more violations than control groups in seven of eight studies. An overall relative risk of 1.88 was found for ADHD status and self-reported motor vehicle collisions, and an overall relative risk of 1.35 was for ADHD status and official citation reports.

In addition, driver simulation studies provide evidence that pharmacological treatment may help to improve driving among individuals with ADHD. Cox and colleagues performed a series of randomized, crossover studies involving driving simulator tests or on-road testing that examined the potential benefits of MPH on driving performance (Cox et al., 2006; Cox, Humphrey, Merkel, Penberthy, & Kovatchev, 2004; Cox, Merkel, Kovatchev, & Seward, 2000). Although the sample sizes were small, the findings showed that MPH improved driving performance of individuals with ADHD in areas including inattentive driving errors for on-road performance, speeding, inappropriate braking, and percentage of missed stops.

Increased Criminality

ADHD in adults has been found to be associated with an increased risk of criminal activity and incarceration. A 1994 epidemiological study of 102 prison inmates found a prevalence of 25% for ADHD, which is more than 5 times greater than that found in the general population (Eyestone & Howell, 1994). A more recent study of 129 prison inmates found that 45% had ADHD as defined by DSM-IV criteria (Rösler et al., 2004). Also, Torgersen, Gjervan, and Rasmussen (2006) and Rasmussen, Almvik, and Levander (2001) found higher rates of arrests and sentencing among ADHD patients in a study of Norwegian adults. Consistent with these estimates, Babinski, Hartsough, and Lambert (1999) found that a history of hyperactivity-impulsivity or early conduct problems was predictive of official arrests and self-reported crimes.

In the United Kingdom, S. Young, Chesney, Sperlinger, Misch, and Collins (2009) estimated a rate of 14% for DSM-IV ADHD with male prisoners. Of particular relevance to this population, they found significantly higher rates of critical incidents (verbal and physical aggression) among those who met full and partial criteria for current ADHD. Furthermore, this association remained significant after controlling for comorbid antisocial personality disorder, suggesting that aspects of ADHD symptoms, such as impulsive behavior, may lead directly to aggressive outbursts in at least some cases of people with ADHD within the criminal justice system. A further as yet unpublished study by Young, Asherson, Murphy, and Gudjonson found that within a secure forensic psychiatric unit in the United Kingdom, there were low rates of ADHD among those with a primary psychotic disorder diagnosis (around 2%), yet very high rates among those with a primary personality disorder diagnosis (around 20%).

These findings have implications for further research assessing whether effective treatment for ADHD, properly implemented, could lead to improved engagement of prisoners with rehabilitation programs and reduced risk of repeat criminality on release. Given the complexity of such cases, it is envisaged that pharmacological treatment would need to be provided in tandem with psychological treatment programs (S. J. Young et al., 2011). In a recent qualitative study that explored the self-reported life-course experiences of adolescents with symptoms of ADHD in a young offender secure unit in the United Kingdom, three main themes were identified. First, adolescents had experienced some form of severe family disruption, such as bereavement, verbal, and physical and/or sexual abuse. Second, they voiced a need to belong; they spoke of feeling excluded from normal family and social life from an early age due to their attentional problems and of behaving aggressively to others due to difficulties in controlling anger or frustration. Third, they suggested benefits from confinement. It provided needed structure and clear expectations, and encouraged them to reflect on their hyperactivity (S. Young, Chesney, et al., 2009). Detailed discussion of the role of ADHD within the criminal justice system can be found elsewhere (S. J. Young et al., 2011)

Comment From the Authors

It is clearly established from follow-up studies that ADHD often persists from childhood through into adolescence and early and later adult life. This is most obvious for the subset of people who have combined type ADHD or HKD as children and who show persistence of similar symptoms and impairments through into adulthood. However, the onset, course, and outcomes of ADHD are highly heterogeneous with a wide range of clinical presentations and impairments. The severity and nature of the impairments depend, at least in part, on the severity of the underlying process. These processes can themselves be modified by social, cultural, and environmental factors, as well as being related to underlying genetic and (nonfamilial) environmental etiological factors and associated neurobiological impairments.

While few would dispute the validity of the ADHD diagnosis when it is severe, it remains controversial, even among mental health practioners, when the behaviors and symptoms merge more closely with those found throughout the general population. For example, the view is sometimes expressed that if people can function in a high-powered jobs (e.g., health care professional, journalist, successful actor), then by definition they cannot have ADHD, even though they may report a number of symptoms and impairments that may reduce their level of work or social function, and are distressed by ADHD symptoms and impact in their quality of life. This perspective is not entirely surprising, as like many other psychopathological disorders, the symptoms and impairments follow a continuous distribution in the general population, and etiological research has yet to define a clear way to distinguish between those with and without the disorder. Furthermore, the impairments may be undervalued because they may not appear to be striking when a cross-sectional perspective is taken (e.g., less impairing than an episode of major depression or psychosis), but they are trait like and therefore present all the time, leading to long-term difficulties in coping and lowered self-esteem.

The major etiological hypothesis that is widely accepted is of polygenic influences combined with environmental risk factors that influence levels of ADHD symptoms. The clinical disorder is defined when the symptoms are sufficiently frequent and impairing to warrant classification as a clinical disorder (Chen et al., 2008; NICE, 2008). However, recent research also indicates that in some cases, moderate to large etiological influences can be exerted by specific chromosomal aberrations (Elia et al., 2010; Lesch et al., 2011; Williams et al., 2010) or extreme environmental risks such as severe early deprivation (S. E. Stevens et al., 2008). Overall, we conclude that what is now required is a better understanding of the nature of the underlying symptoms and impairments in ADHD, the place of ADHD with adult mental health nosology, and the response of ADHD symptoms in adults to different forms of treatment.

In this article, we highlight the many different presentations of ADHD in adults and draw attention also to the broader phenotype, where the most controversies lie among primary care and adult mental health physicians. The findings reported here match the consensus view of experts in the diagnosis and clinical management of ADHD who describe a wide range of impairments that go well beyond the more overt behavioral problems and the most obvious functional difficulties (Asherson, 2005; Ebert, Krause, & Roth-Sackenheim, 2003; Kooij et al., 2010). One problem that has arisen is in relation to the current operational criteria for ADHD that emphasize the behavioral descriptions of ADHD symptoms based on childhood presentations of ADHD (and the common association of ADHD with behavioral problems such as oppositional defiant and conduct disorders). This has led to the common misperception that ADHD is merely a behavioral problem. However, this is far from the truth. ADHD encompasses a range of psychopathological experiences (mental state changes) which lead to more subjective forms of impairment, in addition to the many functional consequences outlined in this article. These include symptoms such as ceaseless and unfocused mental activity, sleep problems, inner restlessness, impatience and mood instability, and difficulties in regulating normal levels of effort and attention. These difficulties may not always be severe enough to cause overt behavioral disturbances and can be consistent with people leading effective and active lives. However, even in those functioning at a high level, ADHD can give rise to increased difficulty coping with aspects of daily life at work, socially, and at home, and significant levels of distress to individuals and their families. One example is the common report of distress from constant mental and physical restlessness and the difficulties people with ADHD have relaxing or falling asleep. A further common complaint is of feeling exhausted from lack of sleep and the constant high levels of effort required overcoming the difficulties people with ADHD have in focusing their thoughts and initiating, organizing, and completing tasks. Many clinicians working with such patients are aware of how often people use alcohol or cannabis as a way of damping down ADHD symptoms in the evening.

Another important consideration is the traitlike course of the symptoms and impairments associated with ADHD. In some cases, the problems related to ADHD may not appear to be particularly impairing when taking a cross-sectional approach; however, it is important to consider the impact of symptoms that are stable and persist over long periods. The cumulative effect of living with such symptoms on a daily basis for many years can be considerable. For this reason, even relatively modest impairments when considered at a single point in time can become disabling or distressing to individuals and their families because of the chronic course. A comparison can be made to mild to moderate depression or anxiety, which usually follows an episodic course with periods of remission. Such conditions are often less impairing than ADHD because of their fluctuating course with periods of remission, yet they do not engender same level of controversy as ADHD. When evaluating the impairments associated with ADHD, it should be taken into account that the disorder starts during childhood or early adolescence and symptoms are experienced on a daily basis for many years, often leading to chronic low self-esteem. While many people can learn to adapt to such a chronic traitlike condition, that does not mean that they do not suffer and may exert considerable effort to overcome the impact of the disorder.

Finally, it is clear from the many reports cited in the literature that there is a considerable burden from the symptoms and impairments of ADHD. We know that even in severe cases, ADHD may be misdiagnosed because adult mental health practioners are not always trained or sufficiently familiar with the typical onset, course, outcomes, and response to treatment for ADHD in adults. Specialist clinics frequently see patients who have been incorrectly diagnosed with a personality or mood disorder, such as bipolar disorder. There are however as yet few studies to systematically evaluate the rate of misdiagnosis, although several published studies report high rates of undiagnosed ADHD within the criminal justice system and among those with a personality disorder diagnosis.

When we consider the broader phenotype, there may be an even greater problem. PCPs for example may have particular difficulty in distinguishing ADHD from other common mental health conditions because they are expecting ADHD to present as a primarily externalizing behavioral condition, whereas many of the symptoms in adults are internalizing and related to difficulties in coping with everyday tasks. The variability of performance seen in many people with ADHD, with the ability to perform well on tasks that hold a high salience value for individuals, can lead to judgmental views that people with ADHD are lazy, unmotivated, or not trying hard enough rather than suffering from a mental health condition. However, as we can see from the literature reported here, there is a high personal and economic cost associated with the condition in adults, including mental health and psychosocial problems.

We conclude that greater efforts are needed to fully understand the presentation of ADHD in adults and to communicate this to professional and lay audiences. The disorder is defined mainly in behavioral terms although we are learning more about the specific psychopathology that underlies the condition and forms a core set of experience reported by many adults with ADHD. More work is needed to match different forms of treatment to individual patient profiles, with clear benefits being described for both pharmacological and psychological interventions (NICE, 2008; S. Young & Myanthi Amarasinghe, 2009). Underlying these efforts is the recognition that effective treatment strategies are available for ADHD, which is one of the most common mental health conditions that adversely affect individuals and society.