In the typical understanding of the term 'overdose' , I'll clear up any ambiguity - No-one has ever suffered a fatality as a result of cannabis intake.
You can theoretically administer a lethal dose, but it's something like the equivalent of smoking your own body weight in weed in one session (many have tried bit failed).
You can OD from drinking too much water. Or ingesting too much sugar, or salt, or caffeine. Many have died from doing so, yet most of us manage to stay well within RDAs.
Weed regularly gets referred to as the 'gateway' drug. I don't subscribe to this (sorry). If you have an addictive personality and or are reckless in life, you will find your way to harmful substances one way or another, be that alcohol or hard drugs - or anything else.
I believe it's personality driven, certainly not cannabis driven.
I do not mean to demean the suffering of those that are caught up in a vicious cycle, alas, the black market will always be there in a criminalised model.