The effects of methylphenidate (MPH) and dextroamphetamine (DEX) on tic severity in 20 boys with ADHD and comorbid Tourette syndrome were investigated in a 9-week, placebo-controlled, double-blind crossover study at the Child Psychiatry Branch, NIMH, Bethesda, MD. Tic severity was significantly greater during treatment with relatively high doses of both MPH (20-25 mg bid) and DEX (12.5-22.5 mg bid). Both stimulants significantly decreased hyperactivity and treatment was continued for 1 to 3 years in 14 of 20 patients. Tic exacerbations were reversible, and MPH was better tolerated than DEX. 
COMMENT. In treatment of ADHD and TS, the lowest effective dose of stimulant should be used, and increases in dosage should be made slowly. MPH appears less likely to induce persistent tic exacerbation than DEX.
Conventional doses of methylphenidate (0.1-0.3 mg/kg) produced dramatic improvement in behavior in children with ADHD and tic disorders, but complete normalization of behavior was not attained even with larger doses of 0.5 mg/kg, in a study at the Department of Psychiatry, SUNY at Stony Brook, NY. 
Weinberg WA et al, University of Texas Southwestern Medical Center, Dallas, TX, refer to the depressive reaction induced by methylphenidate, particularly with larger doses and in children with a genetic vulnerability. A stimulant-induced exacerbation of the neurochemical abnormality underlying depression is proposed as an explanation for seizures complicating MPH treatment of ADHD.