Mood and Psychomotor Tremor Changes following Acute Caffeine Consumption in Moderate and Minimal Caffeine Consumers

Background: The mood and psychomotor effects of caffeine are well documented; however, many previous studies assessing these factors have been carried out on habitual consumers of caffeine. Thus, it is difficult to discern whether beneficial findings are due to the positive effects of caffeine or the reversal of negative withdrawal symptoms. Aims: The current placebo-controlled balanced-crossover study aimed to investigate the acute effects of caffeine on mood and psychomotor performance in both moderate consumers and minimal/nonconsumers of caffeine. Materials and Methods: Following overnight caffeine abstinence (∼12 hours), 15 moderate consumers (mean 316.2 mg/day) and 14 minimal/nonconsumers (mean 37.07 mg/day) received a beverage containing either 150 mg caffeine or a matched placebo at ≥48 hours apart. Mood and psychomotor assessments were carried out at baseline and 30 minutes postdrink. Bond-Lader visual analogue scales (VAS) and caffeine research VAS were used to assess mood, while three simple motion tasks (using an accelerometer device to record dynamic bodily movement) were used to assess psychomotor control. Results: Baseline differences after a night's abstinence were observed for only two outcome measures, with moderate consumers reporting significantly worse headaches and experiencing more tremors on accelerometer Task 2 (holding both arms out to the sides). Following caffeine, ratings of alertness and jitteriness significantly increased and ratings of calmness significantly decreased. Furthermore, accelerometer Task 2 revealed a significant increase in tremor following caffeine compared to when following placebo. It was concluded that these results do not support the withdrawal reversal hypothesis of caffeine consumption but are more indicative of a net effect of caffeine consumption.