Dude, it's not the cannabis, it's the
smoking. It has been proven that smoking cannabis long term will cause the same as smoking cigarettes but the onset will be much earlier/quicker. There are no harmful effects of THC to the brain or body, at least not by ingesting it they way you are. You can't possibly smoke enough marij to "OD", it's physically impossible. THC is so non-damaging to the human body that it was synthesized to 100 to 800 times its natural strength and was being used recreationally in "Spice" (aparently there has been a stop to that). The compound was called HU-210 if you would like to look. HU-210 is Schedule I.
A CT scan is the way to go. Saved my life.

What a crock of fucking shit.
'Nuf said
And just for the record, vaporizing isnt as healthy as people make it seem. It is just a healthier alternative to normal combustion methods. Vaporizing pure (or near pure) THC is the way to go, unless you can get your hands on some medicinal spray (Sativex) or some high potent edibles.