<p>Caffeine is one of the most widely consumed psychoactive substances globally, primarily ingested through coffee and tea. Although moderate intake enhances alertness, cognitive function, and exercise performance through adenosine receptor antagonism and sympathetic activation, excessive consumption is associated with adverse outcomes such as sleep disturbances, anxiety, gastrointestinal discomfort, and electrolyte imbalance. Moreover, adolescents exhibit heightened vulnerability to caffeine’s negative effects, showing strong dose-dependent increases in depressive symptoms and suicidality with frequent energy drink consumption. This review synthesizes current evidence on the bidirectional physiological effects of caffeine and provides a comparative analysis of caffeine content across major caffeinated beverages. Coffee displays substantial variability in caffeine concentration depending on bean species, roasting degree, and extraction method, with Robusta-containing brews consistently exhibiting higher caffeine levels than Arabica. In contrast, tea delivers caffeine alongside modulatory compounds such as L-theanine and catechins, producing a more stable stimulatory profile influenced by fermentation level and processing techniques. Based on these findings, we propose personalized caffeine-intake strategies that optimize beneficial effects while minimizing risks, emphasizing consideration of beverage type, individual metabolic variability, and age-specific susceptibility. This review highlights the need for refined intake guidelines and targeted public-health strategies, particularly for vulnerable populations including adolescents, pregnant women, and individuals with high caffeine sensitivity.</p>