What I'm generally seeing in the literature I could find is that the lethal concentration of cannabis would require ingesting something on the order of up to several hundred pounds in a very short time. Not something that is physically possible. The general conclusion would that cannabis is a substance of very low acute toxicity.To overdose on a substance usually means that there is an intake so large that it is potentially fatal and requires rather urgent hospitalization and specific medical treatment.
Whenever someone is said to have "overdosed", it almost always means that they died as a result.
In that sense, to "overdose" on pot is something very much unheard of.
So if that isn't what you meant by it, I'ld like to know what you meant by it.
May I also remind you that YOU were the one that brought it up, yet you feel like *I* am the one who should clarify? :-S
Of course, individual mileage varies and some individuals may be more susceptible or have contributing conditions that enhance any toxic effects.