RadAway

Rad Away is a chemical solution that bonds with radiation particles and passes them through your system. Takes time to work. It is also a potent diarrhetic. While Rad Away removes the negative effects of radiation, it does not prevent you from becoming irradiated, unlike Rad-X.

Fallout, Fallout 2 and Fallout Tactics
(More about Rad Away in Fallout 3 below)

Fallout 3
In Fallout 3, Rad Away is no longer addictive.

Rad Away website
Rad Away appears to have been featured by a real Rad Away website

The Rad Away website and the associated Nuka-Cola and Enclave Radio websites are not, in fact, official. They were created by a private web-designer. Yet this still plays towards a sub-canon Alternate Reality Game for Fallout.

Appearances
Rad Away appears in all Fallout games.

Anty Rad