Abstract
BACKGROUND: Childhood mental health conditions commonly cooccur, with potential treatment implications. Autistic children frequently experience anxiety and attention deficit/hyperactivity disorder (ADHD). We investigated the implications of this cooccurrence for Cognitive Behavioural Therapy (CBT), a front-line treatment for anxiety in autistic children. We tested whether (1) ADHD predicts anxiety treatment response, (2) ADHD improves in response to anxiety treatment and (3) ADHD improvement is related to reductions in anxiety. METHOD: Autistic children with elevated anxiety (N = 167) enrolled in a multisite, randomised controlled trial comparing standard CBT, autism-adapted CBT and treatment as usual. ADHD symptoms and severity were assessed via a parent-report questionnaire and clinical interview, respectively. Linear regressions (questions 1 and 2) and linear mixed models (question 3) were conducted with adjustments for multiple comparisons. RESULTS: Participants meeting diagnostic criteria for ADHD (62%) had greater pretreatment anxiety severity and anxiety-related functional impairment, particularly at school. ADHD did not moderate anxiety response following CBT. Receiving CBT (standard or adapted) predicted reduction in evaluator-rated ADHD severity, but not parent-reported symptoms. Reduction in anxiety severity predicted reduction in ADHD symptoms and severity. CONCLUSIONS: Existing CBT programmes are suitable for treating anxiety in autistic children with cooccurring ADHD. Future research should identify mechanisms through which CBT for anxiety also mitigates ADHD, with the aim of improving treatment precision and effectiveness.