Start the game and type any one of those cheats when playing the game.

General Cheats:
THUGSTOOLS                 - All Level1 Weapons
PROFESSIONALTOOLS          - All Level2 Weapons
NUTTERTOOLS                - All Level3 Weapons
ASPIRINE                   - Full Health

Cheat Codes:
Start game as usual, open up the console with [~] key and enter the command below (CaSe SeNsItIvE):

sam_iEnableCheats=1

Once enabled, close the console (press [~] again) and bring up the
mainmenu by pressing the [Esc] key - now you can enable the basic
cheatmenu by pressing [F1]. Repeat as often as needed just remember you
have to be in the mainmenu [Esc] to trigger the cheatmenu with [F1]. During gameplay, press [~] for the console and type any of the following codes:

Codes               Effect
---------------------------------
please god        - God Mode
please giveall    - Give All Weapons / Ammo
please killall    - Kill All Monster On Level
please open       - Open All Doors
please fly        - Fly Mode
please ghost      - No Clipping Mode
please invisible  - Invisibility
please tellall    - View All Messages
please refresh    - Restore Energy OR: