Diet Pepsi is a low-calorie carbonate cola, introduced in 1964 as a variant of Pepsi-Cola with no sugar. Its current formula in the United States contains only the artificial sweetener aspartame. The current Canadian formulation contains both aspartame (124mg/355ml) and acesulfame potassium (32mg/355ml). Pepsi does not list on its United States labeling the exact amount of aspartame/Nutrasweet present.