The dose-response, clinical effectiveness, and response prediction in 76 children with ADDH treated with methylphenidate (MPH) were evaluated by a double-blind, placebo-controlled, crossover study at the Department of Psychology, University of Hawaii, Honolulu. Four dose levels (5, 10, 15, and 20 mg) were employed. Effects on classroom functioning, (on-task attention, correct completion of assignments, and teacher ratings), were linear and dose related. Accuracy was enhanced at all dose levels, and task completion was significantly greater at doses above 5 mg. Academic improvement was associated with behavioral gains on teacher ratings. In children failing to respond to low dose MPH, attention changes were responsive to dose increments whereas academic and behavioral improvements failed to occur. A significant subset failed to gain academically from treatment with MPH. 
COMMENT. Methylphenidate is again proven effective in the treatment of children with ADDH, and improvements in behavior, attention, and academic functioning may be expected in a large percentage. Response to MPH is related to the dose, especially in tasks requiring attention. In one subset, however, academic performance is unrelated to attentional and behavioral response to MPH. In another subset, MPH is ineffective in all domains of classroom functioning. A child’s academic functioning is most important in assessing response to methylphenidate and the need for dose increments.
The need for subtyping is stressed by reports of brain structural changes in a group of 15 children with ADDH examined by MRI at the Massachusetts General Hospital.The splenial area of the corpus callosum was smaller in ADDH children compared to normal controls. Age was not a factor. 
Differences in brain glucose metabolism in girls with ADDH compared to boys are reported in PET studies at the National Institute of Mental Health, Bethesda, MD. Global cerebral glucose metabolism in 5 ADDH girls was 15% lower than in 6 normal girls, but was unchanged in ADDH boys compared to normal boys; it was 20% lower in ADDH girls compared to ADDH boys. Adolescents showed no changes in cerebral glucose metabolism. 
Attention deficit hyperactivity disorder in adults is reviewed from the New York State Psychiatric Institute . Placebo-controlled studies of MPH in adults are infrequent and largely disappointing. Psychoactive substance use disorder is commonly associated with diagnoses of ADDH in adults and stimulant medication should be used with caution. Adult ADDH is often a self-diagnosed condition, and an excuse for job failure, divorce etc, according to one practicing psychiatrist.