Its a personal preference. But ive been on perWo for 3 years all different brands through out the years and I never needed to take the max dosage ever and they still work great for me. Example im only taking 2 scoops jack3d and always have. Max dosage is 3 scoops. SP Max im on 1 scoop, 1MR 1 scoop, etc...
It really depends on your tolerance and frequency of use. Obviously, if you are needing more scoops for each workout or you get bad crashes then you should consider taking a break. Although in my own experience I have been using a pre-workout for the past 6-7months. With that said, in that time frame I have only used up 2 tubs of n.o xplode, and working on finishing a tub of hemo rage. I usually train on a empty stomach and only took a prewo at a minimum dosage, 2-3 times a week with 2-3days rest in between. I haven't noticed a tolerance yet.
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good advice. also depends on how often you workout. if you workout 5x a week, u will probably build up a tolerance to stims and would need to take a few weeks off from it to give your adrenals a break. dont want to burn them out