The following are known Action Replay Codes for Classic NES Series: Metroid 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
4c88aa95
41097503
486c255b
cef3918d

Infinite Health
4a6d8a5f
64a8a062
1e2a0294
375935b9