you can bind a key to use an syringe to heal you completely. read description for more info and tutorials of how about it work.
Remember, the good old far cry 2, and do you remember of those syringe that healed you? now you can do it in Garry's mod! (only) just drom FC2 health system in addons, (not the rar file) and launch gmod, type in console: bind "YOUR KEY HERE" "FCheal" and spawn an npc to hurt you, type the key you binded to it, your character will pull out an syringe, which will heal you all your health. have fun using this for zombie map! also, it have 3 entity, 1. a single syrette. to add you 1 syringe cause they are limited to use, 2. syrette upgrade, an first aid kit, using it will get you lot of syringe, 3. a syringe stock, when using give you 3 syringe, and you need to wait 28 seconds to use it again. HOPE YOU ENJOY.