"The other [explanation] is much more basic and probably the best one: It’s just a matter of dose. Most people who develop emphysema due to tobacco smoking do so after smoking one or two or three packs a day for decades. Think for a moment about what you’d be like if you smoked 40 or 60 joints a day for 20 or 30 years — lung damage would probably be the least of your problems. It could be that if someone were courageous enough to smoke that much marijuana...they would get lung damage. They probably wouldn’t care about that lung damage if they got it. But people generally don’t use that much." 4. MYTH: You can't get addicted to weed.

"On the flip side, a risk that many people don’t think about — that I certainly didn’t think about — that turns out to be very real is the risk of dependence and addiction. I honestly didn’t think that marijuana addiction was a real phenomenon, at least not in the same way that addiction to cocaine or heroin or even nicotine is, but it turns out it is.