Start the game with the "+set console 1" command line parameter. Press ~ to display the console window, then type "cheats on" to enable cheat mode. Then, enter one of the following codes in the console window to activate the corresponding cheat function:

Result - Cheat Code
God mode - god
Additional health - health [100 or greater]
Weapon select - weapon_give_[1-10]
Kill all monsters in current level - massacre
Invisibility - notarget
No clipping - mode noclip
Cycle three camera views - cam_toggle
Camera focused on next monster - cam_nextmon
Cycle all characters on level - cam_nextmon
Cycle sidekicks on level - cam_nextsidekick
Screenshot - screenshot
Change game speed, 1.0 is default - timescale [speed]
Level select - map [level name]
Key command binding - bind [key and command]
Select active server - connect [server]
Toggle game engine messages - developer [1 or 0]
Toggle clean map load with no caching - flushmap [1 or 0]
Toggle rendering speed display - r_speeds [1 or 0]
Toggle flat-shaded polygons - r_drawflat [1 or 0]
Toggle lightmaps on surfaces - r_fullbright [1 or 0]
Toggle line drawing - gl_polylines [1 or 0]
Disable cheats - cheats 0