Caffeine expectancies influence the subjective and behavioral effects of caffeine.
OBJECTIVE
This study investigated the independent and interactive effects of caffeine pharmacology and expected effects of caffeine on performance and subjective outcomes.


METHODS
Abstinent coffee drinkers (n = 60) consumed decaffeinated coffee with either 280 mg or 0 mg added caffeine. Caffeine dose was crossed with varying instructions that the coffee would either enhance or impair performance in a 2 x 2 factorial design. Performance, mood, caffeine withdrawal, and negative somatic effects were assessed.


RESULTS
Relative to placebo, caffeine improved reaction time and accuracy on the rapid visual information processing task, a measure of vigilance. However, there was a significant dose by expectancy interaction that revealed that among participants given placebo coffee, "impair" instructions produced better performance than "enhance" instructions. Caffeine also improved psychomotor performance as indicated by a finger tapping task with no main effects of expectancy or interactions. Impair instructions produced greater reports of negative somatic effects than enhance instructions, but only when caffeine was administered.


CONCLUSIONS
Manipulating the expected effects of caffeine altered the behavioral and subjective effects of caffeine. A significant dose by expectancy interaction revealed a somewhat paradoxical outcome in the placebo conditions whereby those told "impair" performed better than those told "enhance." This may reflect compensatory responding as has been observed in similar studies using alcohol (Fillmore et al. Psychopharmacology 115:383-388, 1994). Impair instructions led to greater negative somatic effects only when caffeine was administered supporting the active placebo hypothesis.
Harrell
Paul T
PT
Department of Psychology, American University, 4400 Massachusetts Avenue, NW, Washington, District of Columbia 20016, USA.
Juliano
Laura M
LM
D000339:Affect / Q000187:drug effects*; D001288:Attention / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003069:Coffee / Q000737:chemistry; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000187:drug effects*; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology; D055815:Young Adult
D000697:Central Nervous System Stimulants; D003069:Coffee; D002110:Caffeine