Health care supply and county-level variation in attention-deficit hyperactivity disorder prescription medications

Purpose Although much literature reports small-area variation in medication prescriptions used to treat attention-deficit hyperactivity disorder (ADHD), scant research has examined factors that may drive this variation. We examine, across counties in the USA, whether the use of prescription medications to treat ADHD varies positively with supply-side healthcare characteristics. Methods We retrieved annual prescription data for ADHD medications in 2734 US counties from a nationally representative sample of 35 000 pharmacies in 2001-2003. We used a county-level, multivariable fixed effects analysis to estimate the relation between annual changes in healthcare supply and ADHD medication prescriptions. Methods controlled for time-invariant factors unique to each county as well as ADHD prevalence. Results From 2001 to 2003, retail prescription purchases for ADHD medications increased 33.2%. In the multivariable analysis, ADHD medication prescriptions move positively with an increase in the concentration of total physicians. In addition, ADHD medication prescriptions move inversely with changes in the percentage of non-Hispanic Black population. Conclusions Supply-side healthcare factors may contribute to the rise from 2001 to 2003 in ADHD medication prescriptions. This finding warrants attention because it implies that the relative capacity of the healthcare system may influence population prescription rates. We encourage further exploration of the contribution of the supply-side of the healthcare market to secular changes in ADHD medication prescriptions. Copyright (C) 2011 John Wiley & Sons, Ltd.