Mountain Dew MDX (previously known as "Flavor #516" and "Mountain Dew X") was a Mountain Dew energy drink variant that lasted from November 1st, 2005 and until mid-2007. It was PepsiCo's attempt to compete with Coca-Cola's Vault energy drink.
MDX was the original Mountain Dew flavor formula, but with ingredients added such as maltodextrin, ginseng, taurine, d-ribose, and guarana to give it the energy drink kick. It also had a higher caffeine content than original Mountain Dew, despite having the same basic taste and color.
MDX also had a Sugar-Free variant that was available for sometime from the initial release until mid-2006. It was only available in 14 oz. bottles, unlike regular MDX which was available in 14 oz. and 20 oz. bottles.
- This was one of many attempts at a Mountain Dew energy drink. See "Similar Flavors" in the infobox for more.
- MDX was the pioneering flavor for the Sidekick bottle design, which PepsiCo would incorporate into most of their 20 oz. bottle designs later on in the 2010s, replacing the dome-like design.