Several studies have raised the concern that taking this artificial sweetener long-term might cause memory problems (and others). The results are mixed.
We find studies that show it causes and doesn't cause memory problems in rats. The recent studies show that it doesn't have any effect on a person's memory.
For example, here are a small sample of research studies:
Looking over these and other results, it seems that the risk of getting memory problem from taking aspartame could be possible but not likely. However, if you consume lots of it over long periods of time, anything is possible.
Why not try stevia, a natural sweetener instead? It is natural and 200 to 300 times sweeter than sugar. It has zero calories and a clean sweet taste. It has been in use in Japan for over 20 years (and many other countries) and finally received the GRAS (generally recognized as safe) status in the United States in December 2008.
Revised: November 12, 2009