I recently stopped using anything with caffeine and NutraSweet (Aspartame) in it. I am happy to tell you I HAVE noticed a difference in my anxiety levels. It took a few days for the effects to start, and perhaps for my body to detoxify itself. But I now believe I will avoid these altogether.
I was a diet soda Junky and now am drinking regular (non-caffeine) Pop and lots of flavored water. The results have been worth it for me. Just thought it might help someone else out there.