title: Effects of caffeine in overnight-withdrawn consumers and non-consumers.
abstract: BACKGROUND
  A number of recent studies have suggested that caffeine only improves mood and cognitive performance in regular caffeine consumers who are caffeine withdrawn at test (the "withdrawal hypothesis"). This can be tested by investigating the effects of caffeine in non-consumers of caffeine.
  
  
  OBJECTIVE
  To compare the effects of 2 mg/kg caffeine on mood and cognitive performance in overnight-withdrawn consumers and non-consumers of caffeine.
  
  
  METHODS
  Twenty-five overnight-withdrawn consumers and twenty-five non-consumers of caffeine were tested in a within-subjects design where they were given a drink containing 2 mg/kg caffeine on one test day and placebo on another test day. The order of conditions (caffeine/placebo) was counterbalanced. Mood and performance measures were taken before and after each drink, and pre-drink measures were used as covariates in the analysis of post-drink measures.
  
  
  RESULTS
  Analysis of baseline scores revealed no significant effects of caffeine withdrawal. Caffeine generally improved mood and cognitive performance, relative to placebo, in both subjects groups. These effects did not differ significantly between groups apart from three measures (fewer lapses of attention and ratings of alertness and anxiety) where the effects of caffeine were larger in the non-consumers.
  
  
  CONCLUSIONS
  The present study revealed no negative effects of caffeine withdrawal. Beneficial effects of caffeine were observed in both withdrawn consumers and in non-consumers. Therefore, the withdrawal hypothesis is not an adequate explanation for the effects of caffeine.
authors.affiliation: School of Psychology, Centre for Occupational and Health Psychology, Cardiff University, Cardiff, UK. smithap@cardiff.ac.uk
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Smith
authors.forename: Gary
authors.initials: G
authors.lastname: Christopher
authors.forename: David
authors.initials: D
authors.lastname: Sutherland
mesh_terms: D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects*; D001288:Attention / Q000187:drug effects; D002110:Caffeine / Q000008:administration & dosage* / Q000032:analysis / Q000494:pharmacology*; D003071:Cognition / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D010919:Placebos; D011930:Reaction Time / Q000187:drug effects; D012463:Saliva / Q000737:chemistry; D013375:Substance Withdrawal Syndrome
chemical_list: D010919:Placebos; D002110:Caffeine