Acute effects of caffeine in volunteers with different patterns of regular consumption.
BACKGROUND
The effects of caffeine on mood and performance are well established. One explanation of these effects is that caffeine removes negative effects induced by prior caffeine withdrawal. This was tested here by comparing effects of caffeine in withdrawn consumers and non-consumers (who by definition were not withdrawn).


OBJECTIVE
The present study aimed to determine whether caffeine withdrawal influenced mood and performance by comparing regular consumers who had been withdrawn from caffeine overnight with non-consumers. Following this the effects of acute caffeine challenges were compared in withdrawn consumers and non-consumers. In addition, comparisons were made between those with higher and lower caffeine consumption.


METHODS
One hundred seventy-six volunteers participated in the study. Regular caffeine consumption was assessed by questionnaire and this showed that 56 of the sample did not regularly consume caffeinated beverages. Volunteers were instructed to abstain from caffeine overnight and then completed a baseline session measuring mood and a range of cognitive functions at 08.00 the next day. Following this approximately half of the volunteers were given 1 mg/kg caffeine in a milkshake or water (in the 'no caffeine' condition they were given just the milkshake or water) and the test battery repeated one hour later. A second test battery was carried out at 12.00 and a second caffeine challenge at 13.00. A final test session was carried out at 15.00.


RESULTS
The baseline data revealed little evidence of effects of caffeine withdrawal on performance and mood. In contrast to this, caffeine produced a number of significant improvements in performance. There were some differences in the effects of caffeine on regular and non-consumers, with caffeine tending to reduce reaction time in regular consumers while the opposite was true for non-consumers.


CONCLUSIONS
The present results show little evidence of effects of caffeine withdrawal on performance. In contrast, caffeine challenge produced improvements in aspects of performance and these were often not modified by regular caffeine consumption patterns. The differences in effects of caffeine that were observed between non-consumers and regular consumers were in functions that were unaffected by caffeine withdrawal. These findings show that the observed beneficial effects of caffeine cannot be interpreted in terms of a reversal of caffeine withdrawal.
Hewlett
Paul
P
Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, 63 Park Place, Cardiff, UK.
Smith
Andrew
A
D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects*; D000368:Aged; D000704:Analysis of Variance; D002110:Caffeine / Q000008:administration & dosage*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D004327:Drinking Behavior / Q000187:drug effects / Q000502:physiology; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000187:drug effects; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D010555:Personality Inventory / Q000706:statistics & numerical data; D011597:Psychomotor Performance / Q000187:drug effects*; D013375:Substance Withdrawal Syndrome / Q000209:etiology / Q000503:physiopathology*; D014705:Verbal Behavior / Q000187:drug effects
D000697:Central Nervous System Stimulants; D002110:Caffeine