Comorbidities and costs of adult patients diagnosed with attention-deficit hyperactivity disorder.

INTRODUCTION: The purpose of this retrospective study was to examine the prevalence of comorbidities, resource use, direct medical costs, and the costs associated with missed work for adults diagnosed with attention-deficit hyperactivity disorder (ADHD).

STUDY DESIGN: From a large claims database that captures inpatient, outpatient and prescription drug services, individuals diagnosed with ADHD between the years 1999 and 2001 were retrospectively identified. The ADHD cohort (n = 2252) were matched with a non-ADHD cohort (n = 2252) on a 1 : 1 ratio, based upon age, gender, metropolitan statistical area and type of insurance coverage. The ADHD cohort was compared with the non-ADHD cohort for differences in comorbidities and direct medical costs (inpatient, outpatient and prescription drug costs) using year 2001 prices. Using data from six Fortune 200 employers, time missed from work and costs associated with absenteeism, short-term disability and worker's compensation was examined for a subsample (n = 354) of the employees diagnosed with ADHD. Chi-square and t-statistics were used to compare the ADHD population with the control group with regards to comorbidites and service use. Analysis of covariance and multivariate regressions were used to examine differences in days missed from work, direct medical costs and costs associated with missed work.

RESULTS: Adults diagnosed with ADHD were significantly more likely to have a comorbid diagnosis of asthma (p = 0.0014), anxiety (p < 0.0001), bipolar disorder (p < 0.0001), depression (p < 0.0001), drug or alcohol abuse (p < 0.0001), antisocial disorder (p = 0.0081) or oppositional disorder (p = 0.0022) compared with the control group. Controlling for the impact of comorbidities, adults diagnosed with ADHD had significantly higher outpatient costs (USD 3009 vs USD 1492; p < 0.0001), inpatient costs (USD 1259 vs USD 514; p < 0.0001), prescription drug costs (USD 1673 vs USD 1008; p < 0.0001), and total medical costs (USD 5651 vs USD 2771; p < 0.0001) compared with the non-ADHD cohort. Employees diagnosed with ADHD missed significantly more days due to 'unofficial' absences (4.33 days vs 1.13 days; p < 0.0001).

CONCLUSIONS: The results demonstrate that adults diagnosed with ADHD have a higher prevalence of comorbidities, higher medical costs and more absences than matched individuals without ADHD. These findings suggest that there may be an opportunity for the effective treatment of ADHD to lead to cost-offsets.