Forced-choice versus free-choice procedures: caffeine self-administration in humans.
Methodological comparisons of procedures for drug self-administration are rare. In studies examining the reinforcing effect of caffeine in humans, caffeine self-administration usually has been inferred from performance under forced-choice procedures. In the present experiment, caffeine self-administration via coffee was compared under forced-choice and free-choice conditions; i.e., when subjects were and were not required to use a minimum number of coffees. Ten moderate coffee drinkers (2-7 cups/day) were assigned to forced- and free-choice conditions using a randomized cross-over design. Under each choice condition, subjects completed six independent, double-blind trials, consisting of a 2-day exposure period followed by a 2-day test period. During exposure, subjects consumed either decaffeinated or caffeinated (100 mg/serving) coffee on day 1 and the other coffee on day 2. During the test period, subjects had concurrent access to the same decaffeinated and caffeinated coffees. Under the forced-choice condition, subjects were required to drink at least four cups of coffee per day during the test period. Under the free-choice condition, subjects did not have a minimum-cup requirement. In general, the relative rate at which subjects self-administered caffeinated versus decaffeinated coffee was similar across choice conditions, even though subjects self-administered significantly fewer cups of both coffee types under the free-choice than the forced-choice condition. These results suggest that, at least for caffeine, forced-choice and free-choice procedures produce comparable results. Whether this finding generalizes to a context in which caffeine or another drug is more robustly self-administered, remains to be determined.
Oliveto
A H
AH
Department of Psychiatry, University of Vermont, Burlington 05401.
Hughes
J R
JR
Higgins
S T
ST
Bickel
W K
WK
Pepper
S L
SL
Shea
P J
PJ
Fenwick
J W
JW
D000328:Adult; D001519:Behavior / Q000187:drug effects; D002110:Caffeine / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D003069:Coffee; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000187:drug effects; D012054:Reinforcement, Psychology; D012463:Saliva / Q000737:chemistry / Q000378:metabolism; D012646:Self Administration / Q000523:psychology; D014202:Tremor / Q000139:chemically induced
D003069:Coffee; D002110:Caffeine