title: Reinforcing effects of caffeine and theobromine as found in chocolate.
abstract: BACKGROUND
  Although in a previous study we showed that caffeine and theobromine were the main psychopharmacologically active constituents in a 50-g bar of chocolate, mere activity does not guarantee a role in our liking for the food.
  
  
  OBJECTIVE
  Our aim was to see if liking for a drink repeatedly paired with these amounts of caffeine and theobromine would increase compared to a placebo-paired drink.
  
  
  METHODS
  Participants (n=64) consumed a 'novel' drink + treatment capsule on six non-consecutive mornings using a double-blind, placebo-controlled independent-sample design. Aspects of liking and intensity of various sensory descriptors for these drinks were measured at every drink collection. Treatment capsules contained either an ecologically relevant dose combination of 19-mg caffeine and 250-mg theobromine or a placebo.
  
  
  RESULTS
  Liking for the drink paired with the methylxanthine-containing capsules increased over time compared to the placebo-paired drink. This highly significant effect was confirmed by subjective, retrospective changes in liking for the drink.
  
  
  CONCLUSIONS
  Methylxanthines in amounts found in 50-g chocolate may well contribute to our liking for chocolate, especially to the more acquired taste for dark chocolate.
authors.affiliation: Department of Experimental Psychology, University of Bristol, 8 Woodland Road, Bristol BS8 1TN, UK. henk.smit@bristol.ac.uk
authors.forename: Hendrik J
authors.initials: HJ
authors.lastname: Smit
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Blackburn
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001628:Beverages / Q000032:analysis; D002099:Cacao / Q000737:chemistry*; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D002214:Capsules; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D004311:Double-Blind Method; D005260:Female; D005518:Food Preferences / Q000187:drug effects / Q000502:physiology / Q000523:psychology; D006801:Humans; D008297:Male; D012054:Reinforcement, Psychology; D011795:Surveys and Questionnaires; D013649:Taste / Q000502:physiology; D013805:Theobromine / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D002214:Capsules; D000697:Central Nervous System Stimulants; D002110:Caffeine; D013805:Theobromine