Progressive behavioral response to repeated d-amphetamine challenge: Further evidence for sensitization in humans

Background: Behavioural sensitization is the process whereby intermittent stimulant exposure produces a time-dependent, enduring, and progressive behavioral response. Although animal models of sensitization are well established the phenomenon has been relatively little studied iii humans. In a previous study, we reported enhanced responses following a second as compared to a first amphetamine dose in eye-blink rate and ratings of increased motor activity/energy, increased speech, and elevated mood in normal human volunteers. This current study extends those findings in a new sample of normal volunteers. Methods: Eleven normal human volunteers were administered three single oral doses of d-amphetamine (0.25 mg/kg) at 48-hour intervals, alternating with matched placebo in a randomized double-blind trial. Hourly behavioral ratings included eye-blink I-cite, symptoms (elevated mood, increased speech, increased motor activity/energy energy), and subjective drug effects. Results: Eye-blink rate and increased motor activity/ energy ratings progressively increased following each challenge with the third amphetamine close response significantly greater than all other conditions 4 hours postadministration. Similar although less pronounced, responses were observed for elevated mood and subjective drug effect, Conclusions: These results provide further evidence for sensitization of some amphetamine-induced behaviors in human subjects. (C) 1998 Society of Biological Psychiatry.