Well, there can be a very strong mental impact for some people. Vertigo, drowsiness, or a general "fogginess" common side effects some people experience. This isn't unusual: lots of medications have similar side effects, hence the common waring given on prescriptions about not driving or operating heavy machinery until you're familiar with how your body responds to the medication.

However, those are acute effects that go away as the drug wears off. With long-term use, this type of negative effect often reduces with the increase in tolerance, eventually reaching an equilibrium at some lower level of effect (tolerance works both ways: both negative and positive effects go down as ability to tolerate the drug increases).

Most of the native effects from chronic use of morphine is sociological ("increased risks of being arrested").

That's interesting, thanks. My cousin is a recovering heroin addict, and the mental impact is clear as day. I had not considered that long-term morphine use would be significantly different/better in that regard.