Endocrine and behavioral responses to methylphenidate in normal subjects.

Methylphenidate (0.3 mg/kg) was administered intravenously to 20 normal subjects. Behavioral responses varied considerably among individuals. Both cortisol and growth hormone showed significant increases (p less than 0.001). The adrenocorticotrophic hormone (ACTH) response seemed insufficient to explain the increase in cortisol. For men only, the increase in cortisol correlated positively with the increase in epinephrine (r = 0.77, p less than 0.05) and correlated negatively with baseline cortisol (r = -0.70, p less than 0.05), with increase in growth hormone (r = -0.70, p less than 0.05), and with the increase in "energy" (r = -0.83, p less than 0.01). The growth hormone response varied between the sexes, and for men, the growth hormone correlated with both an increase in "energy" (r = 0.70, p less than 0.05) and "friendliness" (r = 0.68, p less than 0.05). For all subjects, baseline heart rate correlated with the increase in "energy" (r = -0.69, p less than 0.002). In a separate study, six male subjects received, on different occasions, saline and a lower dose of methylphenidate. Together, these studies show that the increases in cortisol, growth hormone, and epinephrine, and the decrease in prolactin are dose-dependent.