Aspartame is probably the most thoroughly tested food ingredient or food that we consume today. There are an enormous number of studies that support the ingredient's safety. Here are some key papers:
Aspartame: A Safety Evaluation Based on Current Use Levels, Regulations, and Toxicological and Epidemiological Studies.

B.A. Magnuson, G.A. Burdock, J. Doull, R.M. Kroes, G.M. Marsh, M.W. Pariza, P. S. Spencer, W.J. Waddell, R. Walker, and G.M. Williams.
Critical Reviews in Toxicology, 37, 629-727.

This comprehensive review of the scientific research studies on aspartame concludes that there is no evidence that the low-calorie sweetener is linked to health problems. The researchers reviewed more than 500 reports.

A significant part of the study involved an analysis to estimate current consumption levels of aspartame. The panel found that consumption, which averages 4.9mg/kg/day, is a fraction of the ADI (Acceptable Daily Intake) for aspartame, which is set at 50mg/kg/day. Even among those with the highest intake, consumption remains considerably below this level.

As well as studies involving healthy adults and children, studies have also examined the potential effects of aspartame on adults and children with diabetes, children who are hyperactive or claiming to be sugar-sensitive, and people with Parkinson's disease and depression.

The paper concludes that aspartame is safe. There is no credible evidence that aspartame has any adverse effects, even when consumed at many times the ADI.

Click here to read the abstract of the paper.

Safety of long-term large doses of aspartame.

A.S Leon, D.B. Hunninghake, C. Bell, D.K. Rassin DK, T.R. Tephly.
Archives of Internal Medicine. 149(10), 2318-2324.

There is extensive evidence from studies conducted with human volunteers that aspartame has no adverse effects. The researchers in this study gave participants the amount of aspartame equivalent to that found in 30 cans of diet soft drink, every day for a period of six months. There were no adverse effects.

Click here to read the abstract of the paper.

Aspartame: review of safety.

H.H. Butchko, W.W. Stargel, C.P. Comer, D.A. Mayhew, C Benninger, G.L. Blackburn, L.M. de Sonneville, R.S. Geha, Z. Hertelendy, A. Koestner, A.S. Leon, G.U. Liepa, K.E. McMartin, C.L. Mendenhall, I.C. Munro, E.J. Novotny, A.G. Renwick, S.S. Schiffman, D.L. Schomer, B.A. Shaywitz, P.A. Spiers, T.R. Tephly, J.A. Thomas, F.K. Trefz.
Regulatory Toxicology and Pharmacology 35 (2 Pt 2), 1-93

This paper reviews the extensive work that was conducted to establish the safety of aspartame before its approval in the United States in 1981, and to address questions that were raised after products with aspartame were on the market. The authors conclude that there are no unresolved questions about aspartame.

Click here to read the abstract of the paper.