> Forgive my ignorance, but I’ve never been clear on the distinction between “psychologically addictive” and “physiologically addictive”.

Quit cigs/caffeine and you'll be irritable and nothing much else... maybe constipated for the first days? Quit heroin and you will likely stop to function, your brain needs it. Same as alcohol, real alcoholics don't stop cold turkey or they will likely die, their body needs it. As the substances have replaced their natural counterparts which the body has forgot how to make.