INTERACTION OF EXPECTANCY AND THE PHARMACOLOGICAL EFFECTS OF D-AMPHETAMINE - SUBJECTIVE EFFECTS AND SELF-ADMINISTRATION

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.