caffeine + quercetin

**Caffeine + quercetin** is a combination of two small molecule compounds: caffeine, a well-known central nervous system stimulant, and quercetin, a dietary flavonoid commonly found in plants. Both compounds act as antagonists of adenosine receptors. Caffeine is widely recognized for increasing alertness and reducing fatigue by blocking adenosine receptors in the brain, thereby enhancing vigilance and mood[1]. Quercetin, in high doses (as in supplements, not diet), also exhibits adenosine receptor antagonism in vitro and is marketed for purported "caffeine-like" stimulant effects, although human studies show that quercetin alone does not significantly impact vigilance or mood at typical supplement doses and its effects are generally weaker than caffeine[1]. Quercetin is a potent inhibitor of the cytochrome P450 1A2 (CYP1A2) enzyme; co-administration with caffeine significantly inhibits caffeine metabolism by reducing CYP1A2 activity, thus potentially increasing caffeine exposure and prolonging its effects[2]. This interaction is independent of common CYP1A2 gene polymorphisms[2].