There is actually a bad end that results from having the parasites on you, but you need to trigger a certain event to have it happen. I'd rather not have a time limit on removing them, unless it's within a constrained environment, as otherwise it's really unfair. Plus, some people just want to go through the game wearing them as long as possible.
Drugs/addiction, probably not. It's a touchy subject, and not something I really want to delve into in a game like this. The exception would probably be something like becoming addicted to an NPC's fluids or something and having to have sex with them regularly to function XD.