Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users.
BACKGROUND
Caffeine produces mild psychostimulant effects that are thought to underlie its widespread use. However, the direct effects of caffeine are difficult to evaluate in regular users of caffeine because of tolerance and withdrawal. Indeed, some researchers hypothesize that the psychostimulant effects of caffeine are due largely to the reversal of withdrawal and question whether there are direct effects of caffeine consumption upon mood, alertness, or mental performance in nondependent individuals.


OBJECTIVE
This study investigated the physiological, subjective, and behavioral effects of 0, 50, 150, and 450 mg caffeine in 102 light, nondependent caffeine users.


METHODS
Using a within-subjects design, subjects participated in four experimental sessions, in which they received each of the four drug conditions in random order under double blind conditions. Participants completed subjective effects questionnaires and vital signs were measured before and at repeated time points after drug administration. Forty minutes after the capsules were ingested, subjects completed behavioral tasks that included tests of sustained attention, short-term memory, psychomotor performance, and behavioral inhibition.


RESULTS
Caffeine significantly increased blood pressure, and produced feelings of arousal, positive mood, and high. Caffeine increased the number of hits and decreased reaction times in a vigilance task, but impaired performance on a memory task.


CONCLUSIONS
We confirm that acute doses of caffeine, at levels typically found in a cup of coffee, produce stimulant-like subjective effects and enhance performance in light, nondependent caffeine users. These findings support the idea that the drug has psychoactive effects even in the absence of withdrawal.
Childs
Emma
E
The University of Chicago, 5841 S Maryland Avenue, MC3077, Chicago, IL 60637, USA.
de Wit
Harriet
H
D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects; D001143:Arousal / Q000187:drug effects; D001519:Behavior / Q000187:drug effects*; D002110:Caffeine / Q000009:adverse effects / Q000493:pharmacokinetics / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000009:adverse effects / Q000493:pharmacokinetics / Q000494:pharmacology*; D003913:Dextroamphetamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000187:drug effects; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects; D012463:Saliva / Q000737:chemistry / Q000378:metabolism; D019966:Substance-Related Disorders / Q000523:psychology; D011795:Surveys and Questionnaires
D000697:Central Nervous System Stimulants; D002110:Caffeine; D003913:Dextroamphetamine