[Blarg]

It can cause similar spaciness and head/neck aches as phenyalanine, one of its components, can, so it's not completely invisible in its effect on many people. However, that effect varies from person to person too, and is dependent on how much you've already consumed.

I find it can interfere with my digestion if I take too much, and it can give me the spacey thing and occasionally a really tight neck and/or headaches. I'll still drink diet sodas, but I can't say I feel smart for doing it.