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Sports-nutrition reviews confirm that among the ingredients on the label — caffeine, taurine, B vitamins, sugar — caffeine carries essentially all of the demonstrated stimulant effect, kicking in around 3 mg/kg. Taurine has interesting mechanistic leads, but the same reviews note the results are inconsistent from one study to the next. B vitamins are present in amounts far beyond daily needs; they're water-soluble and simply flushed out if you're not actually low. A controlled trial on Monster Energy specifically found a higher resting heart rate after the can with no improvement in time-to-exhaustion — your body reacts, but performance doesn't necessarily follow. The sugar (up to 54 g in a 500 mL can) adds its own glucose spike, and combined with caffeine has a documented effect on blood pressure. So the real mechanism holds for caffeine, stays murky for taurine, and the sugar is the actual stowaway behind the crash that follows.
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