On June 30, 1998, the artificial sweetener acesulfame potassium (Ace-K) was approved for use by the Food and Drug Administration. PepsiCo responded within one hour, announcing the introduction of Pepsi ONE (which reached store shelves the following October). This new variety was based upon an earlier product (sold in other countries) called Pepsi Max, but it featured a formula and flavor profile developed specifically for the U.S. market.
After several years of declining sales, a new formula was introduced in early 2005, replacing aspartame with Splenda brand sucralose. (Acesulfame potassium remained the secondary sweetener.) This change was accompanied by new packaging and a new advertising campaign. The same year, Pepsi's long-time rival launched Coca-Cola Zero (sweetened with aspartame and acesulfame potassium) and Diet Coke with Splenda.
The current Pepsi ONE ingredients are: carbonated water, caramel color, natural and artificial flavors, phosphoric acid, potassium benzoate (preservative), sucralose (Splenda brand), caffeine, citric acid, and acesulfame potassium.
A can of Pepsi One includes 55.5 mg of caffeine, more than in one can of Mountain Dew.