I don't see how you could possibly overdose on kratom - large doses make you sick (and when I say "large dose", I mean relative to a typical dose of 3-10g - which is nowhere near to an overdose). I don't have a source (on mobile), but I seem to recall reading that you'd need to eat something like a kg if kratom to overdose.

Both cannabis and kratom can be psychologically addictive, in the same way as anything "rewarding" can be.

As kratom contains opioids, it might also cause physical dependence. I say might, as mitragynine is not a typical opioid, in that it doesn't recruit beta-arresting - which is thought to be responsible for the build up of tolerance and dependence by opioids, as well as for some of the negative side effects, such as respiratory depression.

There are many conflicting anecdotal reports claiming that kratom does cause withdrawal on abstinence, or does not. Personally, I have previously been able to stop kratom multiple times with no withdrawal at all (which has certainly not been the case with my prescribed opioid meds). My guess is there may be genetic factors at play here, and of course as a natural product there are bound to be variations in chemical composition of kratom from different sources.