title: Cognitive and psychomotor performance, mood, and pressor effects of caffeine after 4, 6 and 8 h caffeine abstinence.
abstract: BACKGROUND
  Many studies have found that caffeine consumed after overnight caffeine abstinence improves cognitive performance and mood. Much less is known, however, about the effects of caffeine after shorter periods of caffeine abstinence.
  
  
  OBJECTIVE
  The aim of this study was to measure the effects on psychomotor and cognitive performance, mood, hand steadiness, blood pressure and heart rate of caffeine administration after periods of 4, 6, and 8 h of caffeine abstinence.
  
  
  METHODS
  Participants (n = 49, 27 female) were moderate to moderate-high caffeine consumers (mean daily intake 370 mg/day). Following overnight caffeine abstinence, a 'pre-dose' of caffeine (1.2 mg/kg) was administered at 9 A.M, 11 A.M or 1 P.M. The participants started a baseline battery of measurements at 4 P.M.: before receiving caffeine (1.2 mg/kg) or placebo at 5 P.M.: They then performed the battery of tests again, starting at 5:30 P.M. This was a double-blind, placebo-controlled, randomised study.
  
  
  RESULTS
  Performance and mood measurements confirmed a psychostimulant action of caffeine (versus placebo), but only after 8 h of caffeine abstinence. Caffeine also increased blood pressure after 8-h abstinence, whereas hand steadiness was decreased and perception of task demand was increased by caffeine after 4 h, but not after 6- and 8-h abstinence.
  
  
  CONCLUSIONS
  A second cup-of-coffee equivalent dose of caffeine only reliably affected cognitive performance and mood after an 8-h interval between doses, but not after shorter intervals (when caffeine had some adverse effects). These results show that, apart from caffeine consumption soon after waking, the daily pattern of caffeine intake of many typical caffeine consumers is not well explained by the short-term psychostimulant effects of caffeine.
authors.affiliation: Department of Experimental Psychology, University of Bristol, 8 Woodland Road, Bristol, BS8 1TN, UK, peter.rogers@bristol.ac.uk.
authors.forename: Susan V
authors.initials: SV
authors.lastname: Heatherley
authors.forename: Robert C
authors.initials: RC
authors.lastname: Hayward
authors.forename: Helen E
authors.initials: HE
authors.lastname: Seers
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Rogers
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000339:Affect / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002110:Caffeine / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics; D003071:Cognition / Q000187:drug effects* / Q000502:physiology; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D006225:Hand / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology* / Q000523:psychology; D013647:Task Performance and Analysis; D013695:Temperance; D013997:Time Factors; D014202:Tremor / Q000139:chemically induced / Q000503:physiopathology
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine