Not really, I've done a lot of hard drugs, except heroin/opioids/benzos, and I'd say caffeine is the hardest to quit. Literally been on a 3 day binger awake and couldn't figure out why my head hurt, thought it was food, water, oh
no whoops it was a caffeine withdrawal.
Everything else I can do on and off, some things it's been years, caffeine I've only quit once. Lapsed and haven't been able to again.
I was specifically thinking of heroin and friends which can have massive withdrawal symptoms and need plenty of external support to overcome. “all illicit” is too big an umbrella I agree. Change that to “some” instead “a lot”.
Everything else I can do on and off, some things it's been years, caffeine I've only quit once. Lapsed and haven't been able to again.