It is difficult to identify the component of energy drinks responsible for the above-described effects, because most studies do not include the multiple control groups that would be needed to compare the energy drink or shot to each of its listed ingredients. However, caffeine is a likely candidate, because its benefits — improved cognitive function and exercise performance, etc. — and adverse effects — elevated heart rate and blood pressure, sleep disturbance, headaches, etc. — are almost identical to those caused by energy drinks. For more information, please read our article: How does caffeine work?.
In addition to caffeine, energy drinks also typically contain sugar, which might contribute to the exercise-performance-enhancing effect of energy drinks and shots that has been documented in some studies.[1] However, the sugar content of energy drinks is highly variable (1–63 grams; 19.9±18.2 grams on average),[1][2] and further studies are needed to understand the contribution of energy drinks’ sugar content to the claimed effects.
Many other ingredients are added to energy drinks and shots: taurine, glucuronolactone, carnitine, choline, electrolytes, vitamin A, vitamin C, vitamin D, and vitamins B3 (niacin), B6, and B12. The known effects of these ingredients do not align with the claimed benefits of energy drinks and shots. That said, some studies have found greater disturbances in blood pressure and in the heart’s electrical activity after consumption of an energy drink than after a drink containing identical amounts of caffeine, but lacking the energy drink’s other ingredients.[3][4] This suggests that some energy drink ingredients besides caffeine may also have detrimental effects. However, the problem is that most studies simply compare an energy drink to water, rather than having a control group for each ingredient (e.g., energy drink vs. water, vs. water+caffeine, vs. water+taurine, vs. water+sugar, etc.). Therefore, the additional ingredients in energy drinks have not been studied in adequate detail to fully understand their benefits or risks, or the lack thereof.[5] Consequently, further high-quality research is necessary to fully understand how energy drinks cause their benefits and drawbacks.