Same caffeine dose, different capsule, and only guarana produced a statistically significant boost in peak power. In a randomized crossover trial of 18 active men, guarana raised peak power output by 4.0% over placebo while anhydrous caffeine did not reach significance. But here's the catch: guarana didn't significantly beat caffeine head-to-head, and the differences between them were only descriptive. Here's what the numbers show, where the study falls short, and how to dose guarana by caffeine content if you want to try it.
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