The following are known Action Replay Codes for Looney Tunes: Back in Action on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
6d025ad4
a0435dc9
c05cdcd0
a873c2a2

Infinite Energy
8e10b0f7
7f184534

Infinite Lives
41612b27
fed2ec58