Neurocognitive effects of methylphenidate in adult attention-deficit/hyperactivity disorder

Rationale: Features of childhood attention-deficit/hyperactivity disorder (ADHD) often persist into adulthood. It has been shown that adult ADHD is associated with various neurocognitive deficits, including impairments in spatial working memory (SWM) and attention. It is not known whether these deficits are ameliorated by methylphenidate in adult ADHD. Objectives: The aim of this study was to evaluate the neurocognitive effects of a single dose of methylphenidate on SWM, visual memory, spatial span and sustained attention in adult ADHD. Methods: Twenty-four adult patients, recruited from a specialised clinic for the assessment of adult ADHD, were entered into a double-blind, randomised, placebo-controlled crossover study using a single 30 mg dose of methylphenidate. Results: Eighteen patients met DSM-IV criteria for adult ADHD. Methylphenidate resulted in an improvement in SWM performance and sustained attention, together with a speeding in response time, in these patients. Six patients with attentional difficulties, who did not meet a DSM-IV diagnosis of ADHD, showed a different pattern of response to methylphenidate compared to the ADHD group. For the combined group, moderate correlations were shown between childhood ratings of ADHD (both self-reported and informant ratings) and response to methylphenidate on the SWM task. Conclusions: Adults with ADHD had a similar neurocognitive response to methylphenidate to that previously reported for childhood ADHD. Our results provide further support for the validity of the ADHD syndrome as defined by DSM-IV and indicate possible neurocognitive substrates for clinical improvement with chronic methylphenidate.