The effects of methylphenidate (MPH) on the immune system was studied in laboratory mice and in 6 healthy boys treated for ADHD with 30-45 mg/day MPH at the Kings County Hospital, Brooklyn, NY. In mice, MPH (1, 5, or 10 mg/kg) reduced by up to 63% numbers of T-helper/inducer cells and also IgG+ cells in the spleen and increased up to 400-fold the serum levels of IgG (ELISA), both in a dose-dependent pattern. Three of 6 boys had twofold increases in IgE levels (188-285 IU/mL). MPH induced a marked hypersensitivity to mitogen-induced proliferation of lymphocytes, a hypergammaglobulinemia, and increased IgE levels. 
COMMENT. The apparent immunological effects of methylphenidate suggested by these studies is a disturbing finding which should discourage the use of larger and more toxic doses of MPH in the treatment of ADHD. Further investigations of this MPH-induced immune system hyperactivity are indicated, especially in children with IgE-mediated asthma, allergic rhinitis, and other atopic diseases, in HIV infected children, and its possible interference with immunizations and the normal maturation of the immune system in young children. Drugs used in asthma have been implicated in causation of ADHD. We are now concerned with the possible effects of stimulant treatment of ADHD on the outcome of asthmatic and other allergic disorders.