title: Caffeine self-administration in humans: 2. A within-subjects comparison of coffee and cola vehicles.
abstract: The reinforcing effects of caffeine ingested in coffee versus cola were studied. Eleven participants who drank both coffee and cola (3-10 cups of coffee and 1-6 cans of cola daily; M = 632 mg caffeine/day) were tested in 4 conditions: cola at 33 mg/serving (the usual dose), coffee at 33 mg/serving, cola at 100 mg/serving, and coffee at 100 mg/serving (the usual dose). Each condition consisted of 6 double-blind weekly trials. In each trial, participants sampled caffeinated and noncaffeinated beverages and then had concurrent access to the 2 beverages. Relative use of these beverages was used to assess caffeine reinforcement. Across the 4 conditions (24 weeks), reliable caffeine reinforcement occurred in 5 participants (45%). Caffeine reinforcement did not differ as a function of vehicle or serving dose, and no vehicle-dose interactions were found. With both cola and coffee at the commonly used doses, self-reported motivation to work was greater and drowsiness and laziness smaller with caffeinated than noncaffeinated beverages. Results indicate that, among users of both coffee and cola, caffeine self-administration and subjective effects occur with both vehicles.
authors.affiliation: Department of Psychiatry, University of Vermont, Burlington 05401-1419, USA.
authors.forename: A
authors.initials: A
authors.lastname: Liguori
authors.forename: J R
authors.initials: JR
authors.lastname: Hughes
mesh_terms: D000328:Adult; D000339:Affect / Q000187:drug effects; D001519:Behavior / Q000187:drug effects; D001628:Beverages; D002110:Caffeine / Q000008:administration & dosage* / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage* / Q000494:pharmacology*; D003069:Coffee; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000187:drug effects; D012054:Reinforcement, Psychology; D012646:Self Administration; D019966:Substance-Related Disorders / Q000523:psychology; D013649:Taste; D014202:Tremor / Q000139:chemically induced / Q000503:physiopathology
chemical_list: D000697:Central Nervous System Stimulants; D003069:Coffee; D002110:Caffeine