Yeh, have heard of things from headaches to cramps but I don't think they have ever proven anything. I'm pretty sure it is not a banned substance for the Olympics. I remember when it first came out and everybody was like "wooooooooooo" and it had the price tag to match. A lot of the companies have now even dropped it as a product because the bigger companies know have it combined with other products with names that made my head spin so I lost interest. Funnily enough I did fine without it all and figured there was no substitute for hard work and consistancy...