Dosage effects and individual responsivity to methylphenidate in attention deficit disorder.

Effects of three dosages of methylphenidate (0.15, 0.30 and 0.60 mg/kg) were assessed in 19 ADD-H children on a variety of cognitive, academic and behavioral measures in the laboratory and the classroom. A predominant linear pattern of improvement was found across almost all measures. A slight decrease between 0.3 and 0.6 mg/kg on one cognitive task leaves open the possibility that higher dosages reduce stimulant effectiveness or cause decrements on some kinds of "high-level/high load" tasks. Response patterns of individual children varied considerably across measures. All children improved on at least several measures. Results were interpreted as evidence for stimulant activation of self-regulatory processes.