he's pulling out from jack herer's book which was written around 1990. tashkin was actually hired by our gov to research various effects of cannabisfor a long time now. you would think he would be bias, esp being funded by the gov, and he has found some evidence of cellular damage, etc, but could only suggest that this evidence may be linked to respiratory problems, and other ailments. but recently this year, he presented solid evidence at the american thoracic society that marijuana does NOT cause cancer, even in the heaviest smokers. despite hypothesizing that there would be a positive correlation. in fact the same study managed to provide some weak evidence for a protective effect against lung cancer.

that's my 2c. Ive been working on a marijuana research paper for school, so i'm pretty familar with this guy and his research.