Mountain Dew MDX was an energy drink manufactured and distributed by PepsiCo under the Mountain Dew brand. It was introduced in 2005 as PepsiCo's second attempt to market an energy soda. Josta, the first energy drink introduced by a major soft drink company from 1995 to 1999. "Power Pack" is the marketing term given to the energy ingredients blend in MDX. In June 2005, Coca-Cola started to test-market Vault as an Energy Drink/Soda. Pepsi saw that this was selling well, so Pepsi quickly released their own version before Vault hit stores nationally.
MDX was initially sold in 14 oz. bottles, and was pricier than other Pepsi soft drinks. Due to slow sales, it was relaunched in the fall of 2006 in 20 oz. bottles, and was marketed alongside other Pepsi soft drinks at the same price. The sugar free version had however been discontinued. MDX is still sold in some markets , although it is not as easily found as it previously was.