Depends on the drugs. Some withdrawal symptoms will absolutely kill you. Some drugs like nicotine have barely any side effects, but affect different people differently which can cause other side effects. It’s complicated. One thing for sure, is there is a notable difference between freeing yourself of something, and depriving yourself of something. Most of that happens in your head.

Anecdotally I smoked weed heavily for over a decade and quit cold turkey. I got vivid dreams for a few months, but wasn’t too bothered by it, I wasn’t “depriving” myself of weed. I did need to take a sleeping pill once every other week to finally catch a good night’s rest, but it went back to normal.