The effects of caffeine on psychological functioning

The past few years have witnessed a growing literature on the behavioural, cognitive and performance effects, both beneficial and hazardous, of caffeine ingestion. A brief overview of these studies is provided and methodological difficulties discussed. Disagreement over such factors as the quantity of caffeine required to produce deleterious effects, difficulties obtaining valid measures of caffeine intake from self-reports and differing interpretations of tolerance levels and absorption rates between studies, often prevent the derivation of meaningful results. The need for a rigorous, scientific appraisal of the effects of caffeine on psychological functioning is emphasised. This requires agreement about criteria referred to above, a more valid data base, and in some cases, the adoption of alternative methodology.