In my experience with hard drugs, the human body has an amazing ability to build tolerance, but in a way that biases against positive effects. So, for example,

In my experience with hard drugs, the human body has an amazing ability to build tolerance, but in a way that biases against positive effects. So, for example, a first-time user may consume quantity X of a drug, and get the positive effect Y and negative side-effect Z. An experienced user may consume quantity X and only get a negative side-effect 1/3 or 1/4 Z. But also only get a positive effect of 1/10 Y. So even though the ratio of Z/X has decreased (less negative side-effect per unit of substance) so has the ratio of Y/X (less positive effect per unit of substance). Most importantly, the ratio of Z/Y has increased (more negative side-effect per "unit" of positive effect). I find no reason to disbelieve the existence of performance-enhancing chemicals (or mood-enhancing, or anything else). Perhaps Methylene Blue does do what it's fans think it does -- at first. If you want to get some work done, coffee can really help, Red Bull even more so, and speed even more so. The question is what happens on day 3, week 3, month 3, year 3 of continuous use.