One of the marvels of pre-War medical science, RadAway is a biomedical solution designed to bond with radioactive particles and remove them from the user's system. It effectively purges the body of radiation, but has nasty side effects, including nausea, diarrhea, stomach pains, and headaches. It has to be applied intravenously to work, making it a scary prospect for those afraid of needles.
RadAway removes 300 rads over the course of five seconds and slightly increases thirst and hunger. Greatly increases the chance for disease. Also has a chance to cure mutations.
↑Vault Dweller's Survival Guide p.5-18: "If you have been exposed to large amounts of radiation, then use RadAway to remove the radiation from your system. It won’t feel good, but better a headache and some stomach problems for a couple of days than the long term effects of nuclear radiation! RadAway takes a little while to work."
↑Fallout Official Survival Guide p.124: "RadAway: Used after you have taken radiation damage, this drug will remove some of the contamination from your system. It takes time for the effects to work. There is a chance of developing an addiction to this drug."