title: Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance.
abstract: BACKGROUND
  Despite 100 years of psychopharmacological research, the extent to which caffeine consumption benefits human functioning remains unclear.
  
  
  OBJECTIVE
  To measure the effects of overnight caffeine abstinence and caffeine administration as a function of level of habitual caffeine consumption.
  
  
  METHODS
  Medium-high (n = 212) and non-low (n = 157) caffeine consumers completed self-report measures and computer-based tasks before (starting at 10:30 AM) and after double-blind treatment with either caffeine (100 mg, then 150 mg) or placebo. The first treatment was given at 11:15 AM and the second at 12:45 PM, with post-treatment measures repeated twice between 1:45 PM and 3:30 PM.
  
  
  RESULTS
  Caffeine withdrawal was associated with some detrimental effects at 10:30 AM, and more severe effects, including greater sleepiness, lower mental alertness, and poorer performance on simple reaction time, choice reaction time and recognition memory tasks, later in the afternoon. Caffeine improved these measures in medium-high consumers but, apart from decreasing sleepiness, had little effect on them in non-low consumers. The failure of caffeine to increase mental alertness and improve mental performance in non-low consumers was related to a substantial caffeine-induced increase in anxiety/jitteriness that offset the benefit of decreased sleepiness. Caffeine enhanced physical performance (faster tapping speed and faster simple and choice reaction times) in both medium-high and non-low consumers.
  
  
  CONCLUSIONS
  While caffeine benefits motor performance and tolerance develops to its tendency to increase anxiety/jitteriness, tolerance to its effects on sleepiness means that frequent consumption fails to enhance mental alertness and mental performance.
authors.affiliation: School of Experimental Psychology, University of Bristol, Bristol BS8 1TU, UK. peter.rogers@bristol.ac.uk
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Rogers
authors.forename: Susan V
authors.initials: SV
authors.lastname: Heatherley
authors.forename: Emma L
authors.initials: EL
authors.lastname: Mullings
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D001007:Anxiety / Q000139:chemically induced; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D003071:Cognition / Q000187:drug effects; D003201:Computers; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000187:drug effects*; D011930:Reaction Time / Q000187:drug effects; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology; D013647:Task Performance and Analysis; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine