Diet Pepsi

Diet Pepsi, also called Pepsi Light in some countries, is a carbonated cola soft drink produced by PepsiCo. It is an alternative to Pepsi, containing no sugar, instead using artificial sweeteners (primarily aspartame). First test marketed in 1963 under the name Patio Diet Cola, it was re-branded as Diet Pepsi the following year, becoming the first diet cola to be distributed on a national scale in the United States before expanding internationally. In addition to Diet Pepsi, PepsiCo also produces the low-calorie cola Pepsi Zero Sugar, also called Pepsi Max in some areas, which was developed after Diet Pepsi.

Diet Pepsi was originally test marketed in the United States under the name Patio in 1963. Following a positive reception attributed to the shifting dietary habits and preferences among Baby Boomers, the drink was launched nationally as Diet Pepsi the following year. It became the first diet cola to be distributed on a national scale in the US. The product sold 55 million cases nationally in 1966.

Distribution of the product has since expanded to other countries around the world. Diet Pepsi made its debut in the British market in 1983, where it is also referred to as Pepsi Diet. In many markets however, the beverage is or was marketed under the name Pepsi Light instead, including in Italy, Czechia, Poland, Argentina, Spain Greece, Turkey, Russia, Ukraine, and Brazil. This is not to be confused with a separate "Pepsi Light" that was introduced in the United States in 1975 as a cola with an added taste of lemon.

Diet Pepsi competed primarily with The Coca-Cola Company's Tab in the 1960s and 1970s; however, The Coca-Cola Company introduced Diet Coke in 1982, which has since been the principal competing product to Diet Pepsi. In 1986, Diet Pepsi was the fourth highest selling soft drink in America with a market share of 4.3 percent, one spot under Diet Coke which had 7.1 percent. In 2000, Diet Pepsi had a marginally higher share of 4.7 percent, but placed seventh in the ranking, below Dr Pepper, Sprite, and Mountain Dew (also from PepsiCo) in fourth, while its main competitor Diet Coke remained third. As of 2010, Diet Pepsi represented a 5.3 percent share of all carbonated soft drink sales in the United States, and was ranked as the #7 soft drink brand by volume. In the same year, Diet Coke was recorded as having a 9.9 percent market share.

PepsiCo introduced two further sugar-free cola drinks during the 1990s: Pepsi Max (primarily Europe) in 1993 and then Pepsi One (for the United States) in 1998. Both had a differing formulation compared to Diet Pepsi.

In December 2012, an AP article reported that Diet Pepsi was changing its sweetener to sucralose ahead of a major rebranding of the soft drink that was set for January 2013, but was quietly delayed to August 2015. In that same year, some people on Facebook and Twitter expressed their distaste for the new formula. In response, Pepsi revived its aspartame formulation, as "Diet Pepsi Classic Sweetener Blend" for US markets in September 2016, and it was sold alongside the new formula. PepsiCo later announced plans to revert Diet Pepsi's sweetener from sucralose to aspartame. The new formulation was released marketwide on February 25, 2018.

Additional variations of Diet Pepsi/Pepsi Light have been introduced over the years since the drink's debut, wherein other flavors (such as wild cherry, vanilla, lemon, and lime) have been added to the cola. There is also a variant that has no caffeine: Caffeine-Free Diet Pepsi was the first Diet Pepsi variant and introduced by PepsiCo in 1982. Diet Pepsi Wild Cherry was launched in 1988. Both are still produced today.

In addition, other now-discontinued flavors have existed in the past such as Diet Pepsi Twist/Pepsi Twist Light Lemon (a diet version of Pepsi Twist), Diet Pepsi Vanilla (a diet version of Pepsi Vanilla), Diet Pepsi Lime, the Jazz sub-brand, and a number of limited editions.