Researchers also conducted experiments with cell cultures to try and figure out how Ex-Rad works. It seems to alter how cells deal with DNA damage and suppresses a specific protein (p53) that triggers cell death.
This is one of those "science-fiction predicted it" stories thanks to the Fallout video game franchise. Fallout players have been gulping pills for years to reduce their level of radioactivity and protect against high radiation levels. The drug that protects you from radiation is Fallout is even named Rad-X.