Abstract

Experiments were conducted with 20 subjects on 9 evenings to study the effects of caffeine (150 mg and 300 mg) as compared with placebo upon objective tests of alertness and psychomotor coordination. Simultaneously, mood was assessed by means of a self-rating inventory. The same 20 subjects had also participated in an earlier study on the effects of caffeine upon sleep.

Caffeine had no demonstrable effect upon either objectively measured performance although at the same time it made the subjects feel more alert and physically active.

In some subjects caffeine caused a feeling of nervousness rather than of alertness.

There was a strong positive association between a subject's sensitivity to a mood-elevating effect of caffeine in this experiment and his sensitivity to the wakefulness caused by the drug in earlier experiments on sleep.