Methodological Considerations in Caffeine Research and Depression: A Review of Recent Trends from the Psychological Literature

There has been considerable research into the effects of caffeine on various aspects of human behavior, and it is well understood that caffeine is a mood-altering substance. Research studying the link between caffeine consumption and depression provides a model of investigatory procedures incorporating a large variety of nonexperimental design methods. Thus, a methodological review of the nonexperimental literature was conducted to investigate the numerous methods and measures used to evaluate caffeine's relationship with depression. Through review of the depression-specific literature, a synopsis is provided of how the caffeine-mood link has been investigated when direct observation and manipulation of independent variables has not been feasible.