I use MSG constantly, and I'm one of the people that get headaches if they eat too much of it. Really, you have to so much that the dish starts to taste bad before you get headaches, and I'm pretty sure you build up a tolerance anyways. I will say, while it's a good salt substitute for people looking to lower their sodium intake, you can't replace all of your salt with it. In fact, it's absolutely disgusting if you use it for something other than savoury dishes.