i've been smoking 8 years, and i can tell you tollerance IS real... there's no doubt about it in my mind... sciencetists half the time make an 'assumption' then come back a couple of years later saying they were wrong and found new evidence to support it being the opposite of what they originally thought.... i bet you none of the scientists doing the studying even smoke weed.... which is why they can even come to the conclusion one doesn't exist... if i smoke a bowl after i haven't had weed in a few weeks, i'll be high as hell, let me go through a half oz, and smoke out of the same stash, in the same pipe, i won't even be half as high as that first bowl did....