This thesis intends to examine the use of reaction time within psychopharmacology. Following a review of the literature, an experiment was conducted examining the effects of practise on the Choice Reaction Time (CRT) task utilised by the study centre in which this research was conducted. The results showed that there was a significant effect of practise on the task for both young and elderly populations. This task was then utilised in novel testing situations, in an experiment into the differences in performance between smokers and non-smokers both late into the night and overnight. Findings showed that there were few differences of significance between the two study groups. This research suggested that there is no difference in performance ability of smokers (allowed to smoke as normal) and non-smokers when an occasional late night is required. A further study was then conducted, examining the effects of tea and coffee on this task when used in an intensive testing regime. Four beverages were administered on each study day. A baseline for each beverage was taken, with further testing occurring at 10, 20 and 30 minutes post ingestion as well as at other, less frequent time points throughout the day. There were no results of significance suggesting that the doses of caffeine administered were not large enough to produce a significant change in performance levels, however, the doses we administered enabled the subjects to maintain a constant level of performance throughout the day, with no effects of circadian rhythm being noted. A new reaction time task was then developed according to the theory of Hick (1952). This task was pilot tested in three different modes to see if the task responded as an accurate measure of response latency and which modality of the task was most suited to measuring performance levels. These results showed that the test produced an increase in response latency with each increase in number of stimuli for the Recognition Reaction Time (RRT) aspect of the measure. Further testing was then conducted using this task, utilising the test as a performance measure in the caffeine study (of above), an alcohol study (in healthy young female subjects) and a Ginkgo Biloba Extract (GBE) study (in healthy elderly volunteers). Results from all three studies showed that the increase in number of stimuli increased response latency. High doses of alcohol increased reaction time on this task compared to placebo and the low doses, however there were no differential effects of any of the drugs on the different levels of information processing measured by this task. In conclusion, these data show that the traditional CRT task was unable to illustrate any differences in performance under fatigue in smokers and non-smokers, and also under low doses of caffeine from tea and coffee. When the task was modified to produce a reaction time test according to the theory of Hick, the effects of information load on recognition response speed were clear, however the drugs used in this thesis did not produce differential effects on the processing of information load. Future research using different classes of psychotropic medication has been recommended.