Anti-Radiation Hypo's are a cocktail of chemicals designed to flush radiation from a user's body. They can be found scattered about the world, and can be purchased occasionally from varying Value-Rep stations. They do not, however, drop from enemies, and are therefore limited to location and purchasing.
Radiation is a form of damage that can affect a player. While in an irradiated area, a small bar will begin to fill with green. The longer the player stays, the more the bar will fill. Every few seconds, a portion of this bar will deplete, the screen will flash green, and the player will suffer damage. Even after leaving an irradiated area, the bar will persist until it is fully depleted, and all the damage has been dealt. Rad Hypo's instantly deplete the bar without damaging the player.