Behavioral sensitization is thought to be an important determinant of drug-
taking and drug-seeking behaviors. Although there is abundant research char
acterizing behavioral sensitization in animals, there is little evidence fo
r this phenomenon in humans. The aim of the present study was to determine
if repeated oral d-amphetamine administration enhances self-reported mood a
nd other behavioral indices of d-amphetamine effects in humans. Sixteen hea
lthy volunteers, crith no prior stimulant use, received two doses of d-amph
etamine (20 mg) and two doses of placebo, in alternating order, on 4 consec
utive days, under double-blind conditions. Mood and behavioral effects were
measured using standard self-report questionnaires. Heart rate, blood pres
sure, psychomotor performance, and tapping speed were also monitored. d-Amp
hetamine 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 s
econd d-amphetamine session, the majority of effects were not altered on th
e second session. These results indicate that the subjective effects of d-a
mphetamine display only an apparent mild tolerance after a single exposure
48 h earlier. (C) 1999 Lippincott Williams & Wilkins.