I don't know anything about oral dosages, but I heard it can be worse and easier to overdo it by eating even than smoking. I feel pretty certain that all the bad trips and nasty effects and fears that some people hold of cannabis after maybe one experience as teens, is simply due to way-way-WAY overdoing it. No it won't kill you but like Worth said, the drawbacks of too much MJ do seem to outweigh (if not cancel) the benefits.
Some years ago a friend gave me some pot to try on my problem with tremors. It was fantastic, totally restored my fine motor control, so as long as it lasted I used what I needed to work every day, and then I reckoned up how much I needed per day or per week, and looked into the prescription issue. I was pretty shocked when I saw the amount being licensed for daily use - it was about 100 X the amount that was effective for my dyskinesias and helped me to work.
I went and asked my doctor about it, but at that time anyway, it was not a condition that pot was approved for. Even the smallness of the amount didn't matter. The day it becomes legal and available I will be standing in line to get some for what it's good for.
But seriously, I would be a useless piece of junk if I smoked the amount they think is 'medicinal'.
Work? Lay down like a sack, more like it.
