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Abstract
The current investigation represents the first study designed to evaluate tolerance to stimulant medication among children with Attention-Deficit Hyperactivity Disorder (ADHD) in a school setting. Participants included two-hundred and thirty-seven elementary-aged children (aged 5-12; Mage = 8.1 SD= 1.8). Participants were randomly assigned to receive extended-release methylphenidate (OROS-MPH) either 5-days per week or 7-days per week for the duration of a school year. Monthly teacher ratings of child functioning were used to assess children’s treatment response to pharmacological treatment, and insufficient responders received increased dose adjustments as necessary. The study aimed to investigate (1) whether tolerance developed over the course of the school year (Aim 1); (2) whether randomization to drug holidays (weekend holidays) mitigated the need for dose escalations compared to continuous dosing (7-day-a-week) (Aim 2), and (3) potential individual characteristics as moderators of dose escalation (Aim 3). Tolerance to stimulant medication was observed, as children’s prescribed doses doubled on average by study endpoint. In addition, the group assigned to weekend holidays required fewer dose escalations. Furthermore, children with ADHD and comorbid diagnoses were at an increased risk for requiring higher doses of medication over the school year. These findings support the clinical practice of recommending drug holidays to mitigate tolerance to stimulant medication.