Well I have read every post. Or at least scanned the longer ones.
My 2cents
I have met one smoker out of all the smokers I've known, who seemed to have a real, fiendish, bad, addiction to MJ. It was sad and even us, his fellow smokers, tried to get him to stop, and that's saying something. This guy, on the day we'd run out of weed, would be stumbling around the apartment, and I watched him call a MJ seller 18 times in one day!!! "Dude, one or two calls is plenty"....
Physical, Psychological, I don't know where the line gets drawn. I think it's towards the latter. But this guy was an addict, and he was addicted to MJ.
So I think this is where some are coming from. There are those who are adversly affected, particularly if other, worse druge addictons have been present, the person is going to be very sensitive to that. The dopamine receptors being destroyed is something I have heard about prolonged Cocaine addiction. I've never read about it pertaining the MJ, and yes I have read, read, read, and continue to.
It's hard to separate propaganda (be it left or right) from fact in these studies.
Though I hate righty propaganda, lefty propaganda is a problem too. Talking about saying MJ ain't a drug. If caffeine is a drug, and it is, MJ sure as hell is.
I know productive stoners, and unproductive stoners. Me, I've always had a lazy streak. I'm not going to blame MJ for that. But nor is it right to say it can have no adverse effect on my life. I can't live like a stoner in my 20's, that's a good recipe for diabetes for one thing.
Lastly, one thing that gets forgotten in these discussions, is the huge importance of strain. The difference between a 2-toke couchlock and a soaring sativa is huge. I think one of the reasons the negative stoner stereotype has taken "root" - is the prevalance in some areas of strong indica in commercial pot for its heavy yield and shorter flowering. Smoking nothing but couchlock for recreation, you can see how the stereotype might evolve. It is a different MJ than what young people encountered in the 70's, as the DARE occifer likes to recite. This may be a reason a lot of my younger peeps like to mix tobacco with their weed ("blunts", how disgusting!
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So although the severe addiction is extremely rare with MJ, it happens, and further, I don't know too many stoners who couldn't benefit from getting off their posterior more often and getting more work done!