Effects of caffeine and cyclizine alone and in combination on human performance, subjective effects and EEG activity.

The effects of caffeine and cyclizine alone and in combination, on performance tests and subjective ratings have been examined in two groups of twelve volunteer subjects using a balanced design for order of administration of treatments, a lactose control and with double-blind conditions. In the second study the electroencephalograph (EEG) was recorded after subjective ratings. Results were analysed by analysis of variance and values of < 0.05 taken as significant. Caffeine in doses of 75 to 300 mg increased auditory vigilance compared with lactose dummy. Auditory reaction times were shortened, tapping rates increased and subjects felt more alert. No changes occurred in short term memory, arithmetic or digit symbol substitutions. An increase in energy in the delta band (2.3-4Hz) occurred after caffeine 100 mg. Cyclizine by contrast, produced few changes. Subjects were more alert after 25 mg and more sedated after 100 mg than after dummy. One test only showed impairment: arithmetic, after the 100 mg dose, which also increased energy in the delta frequency band. Combinations of caffeine 100 mg with cyclizine 50 and 100 mg did not produce any subjective changes, or changes in performance tests, differing from lactose. At no time on any test did the performances after combinations of drugs differ from caffeine 100 mg. Performance after both combinations of caffeine and cyclizine differed from that after cyclizine 100 mg on the following tests: vigilance, arithmetic and reaction time, thus showing a tendency for the caffeine effect to predominate. Subjective ratings of sedation after combination of the drugs were intermediate between the ratings following caffeine and cyclizine administered alone.