Sh. Mitchell et al., INTERACTION OF EXPECTANCY AND THE PHARMACOLOGICAL EFFECTS OF D-AMPHETAMINE - SUBJECTIVE EFFECTS AND SELF-ADMINISTRATION, Psychopharmacology, 125(4), 1996, pp. 371-378
The study examined the effects of expectation on the subjective effect
s and oral self-administration of 15 mg d-amphetamine (AMP) and placeb
o in 40 volunteers who reported no prior use of stimulants other than
caffeine. A balanced placebo design was used to create four groups: to
ld Placebo/got Placebo (P/P), told Placebo/got Stimulant (P/S), told S
timulant/got Placebo (S/P), told Stimulant/got Stimulant (S/S). There
were three sessions. On one session (INFO), participants received a ca
psule containing AMP or placebo and were given information about the c
ontents of the capsule according to the balanced placebo design. On an
other session (NO INFO), participants received no information about th
e capsule's contents and were given placebo. On the final session, par
ticipants were allowed to choose either the INFO or NO INFO capsule. P
articipants came to the laboratory to ingest their capsules, and then
returned to their normal environments where they completed subjective
effects questionnaires every 2 h for 8 h. Expectancies influenced the
subjective effects reported during the INFO session, regardless of whe
ther subjects actually received AMP or placebo: subjects who expected
a stimulant had higher ratings of ''feel drug'' and ''like drug''. The
pharmacological effects of AMP were also evident on the INFO sessions
: AMP produced its prototypic subjective effects regardless of subject
s expectancies. Significant interactions between drug and expectancy w
ere obtained on self-report measures of anxiety and arousal: anxiety w
as higher for groups who received substances that did not match their
expectations (P/S and S/P) and arousal increased most in volunteers wh
o expected placebo but received stimulant. Choice of drug was determin
ed primarily by pharmacology: participants who received AMP on the INF
O session usually chose that capsule, regardless of information about
its identity (P/S: 8/10; S/S: 9/10). In contrast, participants who rec
eived placebo on the INFO session chose this capsule at chance levels,
regardless of information about its identity (S/P: 3/10; P/P: 6/10).
Thus, expectancy influenced some of the subjective effects of AMP and
placebo, but the pharmacological effects of the AMP were instrumental
in determining whether volunteers would self-administer the drug.