Epidemiology of treated attention-deficit/hyperactivity disorder (ADHD) across the lifespan in Taiwan: a nationwide population-based longitudinal study.

OBJECTIVES: We used insurance claims of a nationally representative population-based cohort to assess the longitudinal treated prevalence and incidence of attention-deficit/hyperactivity disorder (ADHD) in children, adolescents and adults. METHODS: Participants were identified from among National Health Insurance enrollees in Taiwan from 1999 to 2005. We identified study subjects who had at least one service claim during these years with a principal diagnosis of ADHD. A total of 6,173 patients were recorded in the treated ADHD cohort during the 6-year study. RESULTS: There was a significant increase in the treated prevalence rate of ADHD during the study period, from 64.65 per 100,000 in 2000 to 145.40 per 100,000 in 2005 (p = .001). An increase in the treated incidence rate of ADHD, from 44.67 per 100,000 in 2000 to 81.20 per 100,000 in 2005, was also observed (p = .013). However, the treated prevalence of ADHD was still lower than that of the community data in Taiwan. The peak treated prevalence of ADHD was at age 7-12 years for both males and females, and the peak treated incidence of ADHD was at age 0-6 for females and age 7-12 for males. Overall, the treated incidence and prevalence rates dropped abruptly after age 13-18 (both p<.001) for males and females (p<.001 for both). Male vs. female ratios of treated prevalence and incidence were both above 1 before age 25-30 years, but below 1 thereafter. CONCLUSION: Although an increasing number of people with ADHD sought treatment during 1999-2005 in Taiwan, the treated prevalence of ADHD was still lower than that of the community data. The treated incidence and prevalence of ADHD fell dramatically after age 13-18. However, more women than men sought treatment in adulthood. There may be under-diagnosis and under-treatment of ADHD, especially among females and adults