lung damage

^that's for the toxic does of THC, it doesn't say anything about the other stuff in the smoke, which are likely not as harmless. Like Carbon Monoxide, which can definitely kill (though not from smoking a joint...but it CAN do damage in nonleathal doses).

Like I've said though, it's not something to worry too much about. The worry is probably worse than the smoke anyways.

 

The first quote clearly states that smoking marijuana on a regular basis is less harmful than many other things we use in everyday life, such as aspirin, which is considered reasonably safe. And it's referring to the smoke in general, not JUST theTHC.