title: Do high doses of stimulants impair flexible thinking in attention-deficit hyperactivity disorder?
abstract: OBJECTIVE
  To test the hypothesis that high doses of methylphenidate (MPH) impair cognitive flexibility in attention-deficit hyperactivity disorder (ADHD).
  
  
  METHODS
  A double-blind crossover design was used in an acute dosage trial to assess effects of three dosages (0.3, 0.6, and 0.9 mg/kg) of MPH on the performance of 17 ADHD children on five tasks designed to assess divergent thinking, perseveration, and ability to shift mental set. The tasks also assessed convergent thinking, problem solving, and speed and accuracy of processing.
  
  
  RESULTS
  There was minimal evidence of deleterious effects on flexible thinking or other cognitive processes, either in the ADHD group as a whole or in any subgroup. The most common pattern indicated linear improvement across dosages.
  
  
  CONCLUSIONS
  Under the acute dosage conditions used in this study, MPH doses up to 0.9 mg/kg had an increasingly positive effect on measures of mental flexibility and other cognitive processes. Rather than eliciting perseveration, MPH appeared to improve persistence. The generalized nature of the cognitive and motivational changes observed suggests that MPH acts on central, self-regulatory processes. Because effects of two or more daily doses can accumulate when MPH is prescribed in the clinical situation, clinical doses of more than 0.6 mg/kg were not recommended.
authors.affiliation: Department of Psychology, McGill University-Montreal Children's Hospital Research Institute, Canada.
authors.forename: V I
authors.initials: VI
authors.lastname: Douglas
authors.forename: R G
authors.initials: RG
authors.lastname: Barr
authors.forename: J
authors.initials: J
authors.lastname: Desilets
authors.forename: E
authors.initials: E
authors.lastname: Sherman
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000188:drug therapy* / Q000523:psychology; D002648:Child; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D006801:Humans; D008774:Methylphenidate / Q000008:administration & dosage / Q000009:adverse effects*; D009483:Neuropsychological Tests; D011340:Problem Solving / Q000187:drug effects*; D013850:Thinking / Q000187:drug effects*
chemical_list: D008774:Methylphenidate