To access these cheats, enter L0SR at the Passcode screen. You'll be told the password is invalid. Then do the following:
Full Health and Energy: Start a game, and simultaneously press l and R1 any time during play to replenish your health.
All Weapons and Items: Start a game and simultaneously press p and R1 any time during play to get all the weapons and other items.
Level Passwords:
Level 2: FWQP
Level 3: PLRQ
Level 4: SZNF
Level 5: TD5S
Level 6: J1BT
Level 7: K2CV
Level 8: N3DW
Level 9: 4FX
Level 10: X5GZ
Level 11: C6HO
Level 12: D7J1
Level 13: F8K2
Level 14: FGL3
Level 15: JFM4