•Caffeine may not increase all indexes of arousal or change them in the same way in
•Persons who consume low to moderate doses of caffeine (30 to 450mg) typically
display dose-dependent improvements in indices of arousal, daytime alertness,
vigilance, and some aspects of psychomotor performances and cognitive functions,
such as reactions time, sustained attention, and information processing, and they
experience predominantly positive subjective effects on mood, characterized by
increased well-being, energy and concentration.
•These beneficial effects are particularly evidenced when the individuals are tested
under conditions of caffeine deprivation or total abstinence in regular caffeine users
or following partial or total sleep deprivation.
•As little as 32mg of caffeine has been shown to significantly improve auditory
vigilance and visual reaction time.
•Caffeine can produce an increased capacity for both muscular work and sustained
intellectual effort, but it can also disrupt arithmetic skills and task performance
when delicate muscular coordination and accurate timing are required.
•The effects of caffeine on endurance (and probably other aspects of performance) are
biphasic; that is, lower doses (3-6 mg/kg) enhances performance and higher doses
produce no benefits or decrease performance.
•Several studies on efficiency of information processing in humans have shown that
the effects of caffeine are dependent upon dose, talk demands, the subject’s sex, and
the subject’s typical level of arousal.
•Some studies have concluded that extraoverts (or high impulsives) tend to show dose-
dependent improvements in performance, whereas introverts (or low impulsives)
show improvements with lower doses and decrement with higher doses and other
show no change.
•Other than the conclusion that the behavioural effects of caffeine are quite subtle,
there does not appear to be a consensus as to whether caffeine improves information-
processing efficiency in general.
•It is common belief caffeine can counteract the effects of sedative-hypnotic type
drugs, but the empirical evidence for this belief is equivocal.
•The equivalent of two or three cups of coffee (250mg caffeine) has been shown to
significantly reduce next-day benzodiazepine-induced drowsiness.