Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental condition in childhood, with an estimated worldwide prevalence in children/adolescents ranging from 5.3% to 7.1%, with little variation across countries and regions [1–3]. ADHD is characterized by developmentally inappropriate levels of inattention, hyperactivity, or impulsivity that have a significant impact on different aspects of the child/adolescent’s everyday life, including social, academic, or occupational activities. The severity of ADHD and presence of particular symptoms is highly heterogeneous, and the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5) distinguishes clinical current presentations as predominantly inattentive, predominantly hyperactive/impulsive, or combined when symptoms of inattention or hyperactivity/impulsivity coexist [4]. In addition to the core symptoms, children/adolescents with ADHD have increased rates of comorbidities, including conduct disorder, learning disabilities, oppositional defiant disorder, or depressive disorders, that have further impact on the child/adolescent’s everyday life [5].

ADHD significantly impairs psychosocial functioning and adjustment, and children/adolescents usually have difficulties in interpersonal relationships with peers/family [6, 7]. Furthermore, poor academic performance is more common in children/adolescents with ADHD than in those without ADHD [8]. Consequently, compared with non-ADHD children/adolescents, children/adolescents with ADHD have low self-perception and self-esteem, and impaired quality of life [9–11]. Children/adolescents with ADHD have an increased risk of mortality, and school-age children with ADHD are also more likely to require emergency treatment or be admitted to hospital due to accidental injuries, whereas adolescents with ADHD have higher rates of early and more severe substance use, and of serious delinquent behaviors than their non-ADHD peers [12–15].

Health-economics literature has consistently shown that the overall financial burden of ADHD to children/adolescents, their families, and society is substantial [11, 16–18]. A study on costs of brain disorders in 30 European countries estimated that the direct annual costs of ADHD in 2010 were €781 per person, representing a total of €2546 million. These figures are lower than for autism (total of €15,109 million) and slightly lower than for conduct disorder (total of €3671 million) [19]. Moreover, ADHD annual health care costs per child/adolescent vary substantially across European countries (from €716 in Germany to €2134 in the Netherlands), and are of a similar order of magnitude in the US ($621 to $2720) [11]. However, comparisons are difficult regarding other types of costs; for instance, special educational support may be provided within mainstream schools in some countries (e.g. the UK), but are completely external in others (e.g., Spain).

Systematic reviews of the literature have shown that the pharmacological treatment of ADHD is associated with a substantial benefit in outcomes in the short term, and is cost-effective compared with placebo, no treatment, or behavioral therapy only [20, 21]. Analyses on the effect of treatment on long-term outcomes are scarce, but it has also been reported that untreated individuals experience worse outcomes overall than those receiving any treatment [10, 22, 23]. Therefore, individuals who are untreated or inappropriately treated, or who do not respond adequately to treatment, may experience and/or contribute to a significant increase in the short- and long-term financial burden of the disease as a result of additional expenses that can be attributed to the health, social, educational, and justice systems. There are few studies on the economic impact of ADHD in Europe to date, and those available are not directly comparable with studies published in the US because of putative underlying variations in treatment approaches or public health policies [5].

The objective of this multicenter, cross-sectional study was to estimate the associated direct and indirect costs from both a health care system and a societal perspective over a 1-year time period in Spanish children/adolescents with ADHD. In addition, we assessed whether the characteristics and financial costs differed between children/adolescents responding well (good responders) versus those who responded poorly (poor responders) to currently available pharmacotherapies.

In this study, we evaluated the economic impact of ADHD on the utilization of health care resources and societal costs in Europe as well as the costs of this neurodevelopmental disorder in children/adolescents from the societal perspective. In addition, we assessed how these costs differed between children/adolescents who adequately responded to pharmacological treatment compared with those for whom treatment response was poor.

Although few studies have assessed the economic impact of ADHD on the utilization of health care resources and societal costs in Europe, estimates of costs vary between studies depending on types of services included and methodology. The annual health care costs per child/adolescent with ADHD in Europe (adjusted to 2012 Euros) have been estimated to be between €716 and €3888 [11, 32]. The results of this study are in line with these estimates, with direct medical costs in Spain of €3450.04, accounting for 60.2% of all expenditures. However, it is largely recognized that, unlike many medical diseases, a significant proportion of the financial burden of psychiatric illnesses also arises from indirect costs [33]. The few available studies conducted in the European Union that estimated indirect costs of ADHD found values varying between €50 and €5596 per year, a difference that may be largely explained by the type of services considered [11, 34–36]. In the current study, indirect costs amounted to €2282.60, and were driven mainly by payment to a caregiver.

The main contributor to direct costs corresponded to non-pharmacological interventions (e.g. intervention by an educational psychologist or clinical psychologist), and accounted for 45.2% of total direct costs and 27.2% of total costs. Most cost-of-illness studies in ADHD include these services together with costs of other health care professionals, and therefore the specific weight of costs due to psychological interventions is difficult to compare. Nonetheless, these results are similar to a German study that considered the costs of behavioral therapy separately from other types of interventions, and reported that this expenditure represented 46.6% of costs for children/adolescents aged 6–17 years, and up to 74.4% in children ≤5 years of age [32]. Moreover, we did not consider special education needs, which might have contributed to an underestimation of the total costs in our study. Available European studies (conducted in the UK) that considered the costs of educational needs, such as special school, support teacher, or adapted school curriculum, reported them to be about 3-fold the sum of all other costs [36], or 44% of the total costs [18], and they were estimated to account for 30–40% of all expenditures in the US [16]. Although not directly comparable, our results seem to be in line with these estimates of the high burden due to special educational needs in children/adolescents with ADHD. The average proportion of costs of medication in the present study was 15.5%, which is in line with previous European studies that estimated that they range between 12% and 28.2% [32, 37–39].

One striking finding of our study was the high cost associated with the employment of a caregiver, which represented 65.2% of indirect costs, and 26% of all costs. Mental health-related problems in caregivers and families of children/adolescents with ADHD include stress, anxiety, and depression [40], but the financial burden on caregivers has not been routinely explored [1]. In our study, a parent had to leave their job to care for the child/adolescent in 17.8% of cases, thus hiding a significant unquantified productivity loss. Moreover, this shows that the costs we estimated to caregiving, although high, are largely an underestimation of the actual economic impact on families and society as a whole.

In this study, poor responders were observed to have worse global functioning, and poorer relationships with friends and family. This is in line with the results of several systematic reviews, which reported that treatment has a beneficial effect on multiple short- and long-term outcomes, including self-esteem, social functioning, academic performance, and antisocial behavior, among others, when compared with children/adolescents without ADHD or those with untreated ADHD [10, 22, 23]. Our results, however, also show that beyond symptom control, a poor response to treatment is an important component in the global negative impact of ADHD. This stresses the need for individualized treatment plans to optimize child/adolescent’s outcomes, such as the incorporation of patient-oriented factors (e.g. age, ADHD subtype, comorbidities, and treatment/treatment response history) as well as the preferences and attitudes of children/adolescents and parents/caregivers to pharmacotherapy [41].

Poor responders were found to incur higher total financial expenses than good responders, a difference mainly due to direct medical costs, and particularly because of significantly higher costs of non-pharmacological treatment. Although not directly comparable, these results are in line with previous systematic reviews showing that treatment is associated with less use of ancillary services, including school-, health-, and work-related services; financial assistance services; use of the justice system; and fewer emergency room visits [22, 23].

The main advantage of the current study is that the studied population is representative of different regions in Spain and data were complete for almost all variables studied. However, the results must be interpreted in the light of considerable limitations. First, the cross-sectional nature of the study, with information obtained retrospectively through interview for some variables, means that results may be more sensitive to potential recall bias. Second, children/adolescents recruited in this study were treated by psychiatrists and neuropediatricians, and may therefore be representative of a subset of children/adolescents with more severe ADHD, thus incurring higher costs, as for adults [42]. Third, there are several factors that were not quantified in the study that might have contributed to an underestimation of the total ADHD-related costs. For example, we did not include additional indirect costs such as health-related problems among family members, although these may be considerable too, as suggested by a Dutch study that estimated annual average health care costs per family member as 14.3% of all health care costs [11, 37]. Moreover, we did not estimate costs associated with psychiatric/non-psychiatric comorbidities, which have been shown to cause a 6-fold increase in medical costs compared with ‘pure’ ADHD cases [37]. Although excluding comorbidities can lead to a significant underestimation of the total cost of illness, when it is difficult to separately assess the expenditures of closely related disorders, it can also potentially lead to an inflation of cost estimates [43]. In addition, we did not estimate ADHD-related costs due to the justice system, treatment of comorbid substance abuse, or traffic accidents. None of the available European studies have quantified these totals, but the costs of justice system service needs for children/adolescents with ADHD in the US were estimated to be about 1% of the total costs of ADHD [16].

ADHD is a highly prevalent disorder associated with a significant high personal, familial, and financial impact on the family, health system, and society. An adequate response to pharmacological treatment was associated with lower overall expenses in the management of the disorder.