caffeine and aspartame beverages are just about the most abundantly consumed product in north america... if either of them were dangerous the average life expectancy would become 45 over night.
In fact there is no real evidence that either is harmful to you at all, one keeps you up at night sometimes and the other is the most frequently studied food additive of all time. if they found anything dangerous in it, we would know by now...
http://en.wikipedia.org/wiki/Aspartame_controversy