Effects of expectation and caffeine on arousal, well-being, and reaction time.
The objective of this study is to determine the impact of expectation associated with placebo and caffeine ingestion. We used a three-armed, randomized, double-blind design. Two three-armed experiments varying instruction (true, false, control) investigated the role of expectations of changes in arousal (blood pressure, heart rate), subjective well-being, and reaction time (RT). In Experiment 1 (N = 45), decaffeinated coffee was administered, and expectations were produced in one group by making them believe they had ingested caffeinated coffee. In Experiment 2 (N = 45), caffeinated orange juice was given in both experimental groups, but only one was informed about the true content. In Experiment 1, a significant effect for subjective alertness was found in the placebo treatment compared to the control group. However, for RT and well-being no significant effects were found. In Experiment 2, no significant expectancy effects were found. Caffeine produced large effects for blood pressure in both treatments compared to the control group, but the effects were larger for the false information group. For subjective well-being (alertness, calmness), considerable but nonsignificant changes were found for correctly informed participants, indicating possible additivity of pharmacologic effect and expectations. The results tentatively indicate that placebo and expectancy effects primarily show through introspection.
Schneider
Rainer
R
Institute for Environmental Medicine and Hospital Epidemiology & European Office of the Samueli Institute, University Hospital, Freiburg, Germany. rainer.schneider@uniklinik-freiburg.de
Grüner
Mauritz
M
Heiland
Alexandra
A
Keller
Martina
M
Kujanová
Zuzana
Z
Peper
Martin
M
Riegl
Maximilian
M
Schmidt
Stefan
S
Volz
Petra
P
Walach
Harald
H
D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects*; D001143:Arousal / Q000187:drug effects*; D001794:Blood Pressure / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology*; D003069:Coffee; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D015990:Placebo Effect; D011930:Reaction Time / Q000187:drug effects*; D012718:Set, Psychology
D003069:Coffee; D002110:Caffeine