This study aimed to investigate the effects of high­caffeine energy drink consumption on concentration, anxiety, and vital signs among adolescents. A pretest­posttest design for a single group was employed, and a total of 30 high school female students were recruited. The Learning Immersion Scale for concentration and the Korean State­Trait Anxiety Inventory for anxiety were used. Vital signs, including blood pressure, pulse rate, respiration rate, and body temperature, were assessed. Descriptive statistics were conducted to describe pre­ and post­tests of concentration, anxiety, and vital signs. Paired t tests and Wilcoxon signed rank tests were used to compare differences in pre­ versus post­energy drink consumption for concentration, anxiety, and vital signs in the study. The results indicated that there were significant differences in state anxiety, pulse rate, and body temperature before and after consuming the energy drink. However, there were no significant differences observed in concentration, trait anxiety, systolic and diastolic blood pressure, and respiration rate. This study suggests that high­caffeine energy drinks can increase anxiety but do not have a significant effect on concentration. These findings emphasize the importance of further research to fully understand the potential risks and benefits of energy drinks.