Subjective and behavioral effects of repeated d-amphetamine in humans.

Behavioral sensitization is thought to be an important determinant of drug-taking and drug-seeking behaviors. Although there is abundant research characterizing behavioral sensitization in animals, there is little evidence for this phenomenon in humans. The aim of the present study was to determine if repeated oral d-amphetamine administration enhances self-reported mood and other behavioral indices of d-amphetamine effects in humans. Sixteen healthy volunteers, with no prior stimulant use, received two doses of d-amphetamine (20 mg) and two doses of placebo, in alternating order, on 4 consecutive days, under double-blind conditions. Mood and behavioral effects were measured using standard self-report questionnaires. Heart rate, blood pressure, psychomotor performance, and tapping speed were also monitored. d-Amphetamine elicited prototypical increases on several measures including self-reported drug effects, mood, and physiological responses. However, except for a slight reduction in 'feel drug' scores during the first hour of the second d-amphetamine session, the majority of effects were not altered on the second session. These results indicate that the subjective effects of d-amphetamine display only an apparent mild tolerance after a single exposure 48 h earlier.