Regain 24

Regain 24, more commonly referred to as Regain, is a Japanese energy drink

Usage
Regain was utilized by Solid Snake during his operations in

Behind the scenes
Regain was used as product placement in Metal Gear Solid 4: Guns of the Patriots. When the player drinks it, it recovers their LIFE as well as, depending on the environment it is consumed in, restoring between 25% and 50% of their PSYCHE (for hot environments and cold environments, respectively).

An MGS4-themed commercial premiering around MGS4's development had Solid Snake being knocked down by an explosion, causing the Mk II to arrive with Regain. Snake drinks it and seems to physically restore his youth by doing so. In addition, during development, Regain had a promotional feature where the characters could get tags that included Old Snake, Cyborg Raiden, the Kojima Productions/FOX logo, and a picture of a dog tag containing the FOXHOUND logo.