A nationwide study of attention-deficit/hyperactivity disorder drug use among adults in Iceland 2003-2012

Abstract

In this study, we leveraged on complete nationwide prescription data for the total adult population in Iceland (N = 227,000) to examine how attention-deficit/hyperactivity disorder (ADHD) drugs have been used over the past decade. In particular, we aimed to describe the prevalence, incidence and duration of use of stimulants and atomoxetine, among adults (≥19 years) in Iceland, with regard to sex, age, type of drug and specialty of the prescribing physician. Our results indicate that the 1-year period prevalence of ADHD drug use rose, from 2.9 to 12.2 per 1000 adults between 2003 and 2012, with the most pronounced increases among young adults (19-24 years). The annual incidence increased 3 times, similarly among men and women. Extended-release methylphenidate formulations were the most commonly used ADHD drugs. Specialists in psychiatry initiated treatment in 79% of new adult ADHD drug users. The proportion of users still receiving treatment after 1 year varied from 43.0% (19-24 years), 57.2% (25-49 years) to 47.5% (50+ years). After 3 years, the corresponding proportions still on treatment were 12.4%, 24.5% and 24.3%, and after 5 years 7.9%, 15.9% and 16.8%. These results of increasing ADHD drug use and short treatment durations call for further investigation of the quality of treatment regimens for adults with ADHD and better follow-up of patients treated with ADHD drugs.