ADORA2A and Anxiety: CYP1A2, as already mentioned, and ADORA2A—the gene encoding adenosine receptor A2A (polymorphism at 1976C>T; rs5751876)—are pivotal genes influencing the ergogenic effects of caffeine, with CYP1A2 primarily responsible for caffeine and caffeine derivatives’ metabolism and ADORA2A related to caffeine-induced anxiety effects.