How habitual caffeine consumption and dose influence flavour preference conditioning with caffeine

This study investigated the effects of both habitual caffeine use and dose administered in determining the ability of caffeine to reinforce conditioned changes in flavour preference. Thirty overnight-withdrawn moderate caffeine consumers and 30 non or low-dose caffeine (non/low) consumers evaluated five novel-flavoured fruit teas. Subsequently, their median-rated tea was used in four ensuing conditioning sessions. Either placebo, 1 or 2 mg/kg of caffeine (n=10 consumers, 10 non/low consumers in each condition), was added to the target tea, and all five teas were reevaluated at a final tasting. Pleasantness ratings over the four conditioning sessions indicated that non/low consumers' liking increased for the noncaffeinated fruit tea with no change for the tea containing either 1 or 2 mg/kg of caffeine. Among consumers, pleasantness ratings tended to decrease for the noncaffeinated fruit tea but increased significantly at the 1-mg dose and showed a tendency to increase at the 2-mg dose. Similar effects were shown in the evaluations made before and after conditioning, with no change in the nonexposed drinks. These results show that 1.0 mg/kg of caffeine reinforces changes in flavour pleasantness in acutely withdrawn habitual consumers but not in nonconsumers or nondependent low-caffeine consumers, further endorsing the negative-reinforcement theory of conditioning with caffeine.