Aspartame, which is an artificial sweetener, is also present in Pepsi Max at 77mg. Meanwhile, Diet Pepsi is an older variant introduced in 1964 in the United States. It is branded as a “zero calorie, zero carbohydrates” cola. Its variants include: Diet Pepsi Lime Twist, Diet Pepsi Lemon Twist, Diet Wild Cherry Pepsi. Compared to Pepsi Max, a 7.5 fl.oz bottle/can of Diet Pepsi contains a lower amount of caffeine at 22mg.