There have been several studies that have confirmed the effects of caffeine and the personality dimension of impulsivity (Smith 2002). Performance, according to Smith (2002), is "an interactive function of task difficulty, caffeine and impulsivity" (2002).

Performance on an easy letter cancellation task was improved as caffeine dose increased, but on a difficult task impulsive subjects (less aroused) improved while non-impulsive subjects (more aroused) improved then deteriorated. Other results do not fit this pattern and could reflect other individual differences such as expectancies or caffeine usage (Smith 2002).

Another study conducted by Sawyer, Julia and Turin (1982) showed that caffeine does indeed play a role in behavior, which includes changes in "arousal, anxiety, and performance" (1982). Once again, Sawyer et al. (1982) found that personality plays a big role in caffeine's effects on humans as does sensitivity, adaption to caffeine, and the way that caffeine may interact with both nicotine and alcohol (1982).

Griffiths, Bigelow, and Liebson (1986) conducted a study where nine volunteers with a history of heavy coffee drinking were given coffee in which the caffeine in the coffee had been manipulated under "double-blind conditions by using caffeinated (C) or decaffeinated (D) coffee" (1986). When the subjects were switched alternately for 10 or more consecutive days between C. And D, the daily number of cups consumed tended to be relatively stable (1986). In a different study, the preference for C. versus D. was examined. After researcher-scheduled exposures, volunteers were given the choice between C. And D. When volunteers were presumably caffeine tolerant/dependent, C was rated as being better than D. And was reliably preferred to D. When volunteers were not caffeine tolerant/dependent, C was not reliably preferred to D, nor were there any pronounced differences in ratings in liking (1986). Under these conditions, some volunteers preferred D. To C, stating adverse symptoms (which suggests caffeine toxicity) as reasons for...

The effects of caffeine withdrawal were then studied for 10 or more days. This resulted in an orderly withdrawal syndrome, having an onset latency of 19 hours, peaking on days 1 and 2, decreasing progressively over the next 5 or 6 days (1986). Withdrawal symptoms consisted of headaches, tiredness, laziness, and decreased alertness. The study shows the reinforcing effects of caffeine in humans and documents the severity of caffeine withdrawal syndrome (1986). "It is concluded that caffeine has the cardinal features of a prototypic drug of abuse" (1986).
The fact that caffeine has been proven to have "cardinal features of a prototypic drug of abuse" (Griffiths et al. 1986) should leave no area to wonder if caffeine can significantly alter a person's behavior. While studies have concluded that behavioral changes due to caffeine have more to do with just caffeine ingestion (they have to do with a person's personality, their sensitivity to caffeine, etc.), caffeine can be attributed to anxiety and impulsivity in human beings. Of course there is a difference between consuming a small amount and drinking caffeine excessively; still, research shows that caffeine has been underestimated when it comes to its mood-altering and behavior-changing potential.