The buzz from a Monster Energy comes almost entirely from its caffeine (and the sugar riding along with it) — the taurine and the B-vitamin megadoses on the can don't add a proven benefit beyond that.

noli's read

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.

the sources

No named source held this one up — that absence is part of the verdict.