Every day more than 90% of the world's population consumes caffeine, with global consumption estimated at 120,000 tonnes per year (Burchfield, 1997) and with the world's population drinking such large quantities, the tolerance may develop. Tolerance occurs when an organism no longer responds to the drug and as a result a higher dosage is required to produce the same effects (National Institute of Drug Abuse, 2007). A more precise definition of tolerance according to Baker and Tiffany, as cited in Fernandez, Kluwe, and Cooper (1977) and Kalant, LeBlanc, and Gibbins (1971) is that tolerance represents a rightward shift of the dose-response curve. There are two competing theories, physiological and psychological, that attempt to explain how tolerance develops. Tolerance with respect to physiological theory is divided into pharmacokinetic and pharmacodynamic tolerance. Pharmacokinetic tolerance occurs when there is a decrease in the amount of substance reaching the target area, while pharmacodynamic tolerance occurs because there is a decrease in response to the drug through the cellular mechanism (Open Education Resources, n,d ). Research has found that ethanol works by binding and altering the functions of membrane-bound ion channels and voltage-gated ion channels (Chandler, Harris & Crews, 1998; Harris, 1998; Littleton & Little, 1994; Tabakoff & Hoffman, 1996). The way that drugs like ethanol cause tolerance is that once they exert their action on specific receptor sites, they continue to occupy these receptor sites for a subsequent period of time, thus decreasing the amount of receptor sites that can be stimulated by the drug. same drug at a later time (Siegel, 1975, as cited in Scmidt & Livingstone, 1933) so it always takes more...... middle of paper...... it was expected that after drinking caffeine, Consumers who regularly consumed high levels of caffeine would report smaller changes in energy levels than those who consumed it irregularly. In physiological theory it has also been hypothesized that tolerance is a function of repeated drug administration of the substance. Because the substance caffeine is not present in the decaffeinated condition, it is expected that changes in energy levels in the decaffeinated condition will not differ from those in the rooibos condition. A third hypothesis has been formulated regarding the psychological theory according to which tolerance is a conditioned compensatory response. Because caffeine causes increased energy levels, the decaffeinated group was expected to have lower energy levels than the rooibos group due to factors other than bodily changes..