Aspartame, distributed under several trade names was initially approved in 1981 by the food and drug administration (FDA) after many lab tests demonstrated that it did not cause cancer or other adverse effects in laboratory animals. Questions concerning the safety of aspartame re-emerged in 1996 after a report suggesting that an increase in the number of cases of brain tumors between the years 1975 and 1992 might be actually linked with the introduction and use of this sweetener in the United States. However, an analysis of then-current NCI statistics revealed that the overall incidence of brain and central nervous system cancers had already begun to rise back in 1973, 8 years prior to the approval of aspartame, and continued to rise until 1985. Moreover, increases in overall brain cancer incidence were primarily seen in individuals age 70 and above, a group that was not exposed to the highest doses of aspartame since its introduction.
Then again in 2005, a laboratory study detected more lymphomas and leukemias in rats fed very high doses of aspartame (equivalent to drinking 8 to 2,083 cans of diet soda daily). However, the findings of this study were more or less conflicting. The FDA released a statement regarding this study < http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2006/ucm108650.htm>
Subsequently, it was demonstrated that increasing consumption of aspartame-containing beverages was not associated with the development of lymphoma, leukemia, or brain cancer in human subjects.