Start the game with the -console 1 command line parameter. They, press ~ during game play and type one of the following codes to activate the corresponding effect

god                     God mode
notarget                Invisible to everyone
freecasting             No blood loss when using disciplines
noclip                  No clipping mode
giftxp x                Get x experience points
impulse 101             Most items and weapons
give x                  Spawn an item, weapon or what ever, x might be

                        item_i_written
                        item_g_keyring
                        item_g_eldervitaepack
                        item_g_bluebloodpack
                        item_g_bloodpack
                        item_p_gargoyle_talisman
                        item_p_occult_heal_rate
                        item_p_occult_passive_durations
                        item_p_occult_thaum_damage
                        item_p_occult_dodge
                        item_p_occult_blood_buff
                        item_p_occult_experience
                        item_p_occult_strength
                        item_p_occult_dexterity
                        item_p_occult_obfuscate
                        item_p_occult_presence
                        item_p_occult_lockpicking
                        item_p_occult_frenzy
                        item_p_occult_hacking
                        item_p_occult_regen
                        item_p_research_lg_firearms
                        item_p_research_lg_stealth
                        item_p_research_hg_dodge
                        item_p_research_mg_melee
                        item_p_research_hg_melee
                        item_p_research_lg_dodge
                        item_p_runwonted_rules
                        item_p_research_mg_brawl
                        item_p_research_hg_firearms
                        item_p_research_mg_finance
                        item_p_research_mg_security
                        item_p_research_hg_computers
                        item_p_research_lg_computers
                        item_g_astrolite
                        item_g_wallet
                        item_m_money_envelope
                        item_m_money_clip
                        item_m_wallet
                        item_w_unarmed
                        item_g_lockpick
                        item_a_body_armor
                        item_a_hvy_leather
                        item_a_lt_leather
                        item_a_hvy_cloth
                        item_a_lt_cloth
                        item_d_holy_light
                        item_w_tzimisce3_claw
                        item_w_baton
                        item_w_osnndotnet
                        item_w_tire_iron
                        item_w_severed_arm
                        item_w_torch
                        item_w_sledgehammer
                        item_w_occultblade
                        item_w_knife
                        item_w_katana
                        item_w_fireaxe
                        item_w_fists
                        item_w_claws_protean5
                        item_w_claws_protean4
                        item_w_claws
                        item_w_bush_hook
                        item_w_baseball_bat
                        item_w_flamethrower
                        item_w_thirtyeight
                        item_w_uzi
                        item_w_supershotgun
                        item_w_steyr_aug
                        item_w_remington_m_700
                        item_w_mac_10
                        item_w_ithaca_m_37
                        item_w_deserteagle
                        item_w_glock_17c
                        item_w_crossbow_flaming
                        item_w_crossbow
                        item_w_colt_anaconda
                        item_g_lilly_diary
                        item_g_drugs_pill_bottle
give weapon_physcannon  Crash game
quit                    Exit to the desktop