Caffeine is the most commonly consumed psychostimulant in the world, however, the total effects of the prototypical caffeinated beverages (tea and coffee) have yet to be conclusively linked solely to caffeine content. This thesis assessed the effects of other putative psychoactive components from tea and coffee on measures of mood and performance in humans, both alone and in combination with caffeine, and contrasted these effects between habitual and non-consumers of tea/coffee. For all studies conducted a placebo-controlled, double-blind, balanced-crossover design was used.

GABAa α2-subunit containing receptors are known to be expressed in brain regions associated with anxiety, conditioning and the rewarding properties of drugs of abuse, particularly the amygdala and nucleus accumbens (NAcc). Generation of a GABAa α2-subunit knockout mouse has enabled the role of this subunit to be investigated in these behaviours.