Long-term medication for ADHD and development of cognitive functions in children and adolescents

Objective: Long-term effects of ADHD medication on cognitive functions are not well known. This study investigates development of cognitive functions and ADHD symptoms on well-controlled medication for 1 year in children and adolescents.

Study design: This study is part of an ongoing open uncontrolled trial of long-term medication for ADHD in children and adolescents aged 6-18 years with any form of ADHD, and frequently comorbid autism spectrum disorder (ASD, 29%) or autistic traits (24%). Other comorbidities were oppositional defiant disorder, dyslexia/language disorder, borderline intellectual functioning, developmental coordination disorder. This analysis includes 87 participants (61 boys, 26 girls) who completed Wechsler tests at baseline and after 12 months. ADHD symptoms were investigator-rated on the ADHD Rating Scale-IV at the same time points.

Results: The whole group of children and adolescents showed significant improvements in Wechsler Full Scale IQ (FSIQ, mean at baseline 92.6, at 12 months 97.95), and on the Index Scales Verbal Comprehension, Working Memory and Processing Speed, after one year of well-controlled ADHD medication. Comorbid dyslexia/language impairment predicted a larger rise in FSIQ, but not gender, ADHD presentation or comorbid ASD. Robust improvements in ADHD symptoms were observed (mean ADHD-Rating Scale score at baseline 34.6, and at 12 months 18.3).

Conclusions: Cognitive test scores and ADHD symptoms were improved on well-controlled medication for 1 year in children and adolescents with ADHD, autism and other comorbidities. The main study limitation is the open uncontrolled trial design.