I'm very tolerant to most stims, including those in preworkout formulas, so I was leary about using a stim-free product. But UR has exceeded my expectations & erased any skepticism I had!! It still gave me great energy, focus, and drive, but most importantly, the pain & burning I've always felt from lactic acid buildup was non-existent!! I was able, finally, to push past failure and get those last few muscle-building reps in there!!