Researchers surprised to find no link between marijuana, lung cancer / Study's findings apply even to heavy pot smokers

"The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer.
The new findings 'were against our expectations,' said Dr. Donald Tashkin, a UCLA pulmonologist who has studied marijuana for 30 years.
'We hypothesized that there would be a positive association between marijuana use and lung cancer and that the association would be more positive with heavier use,' he said. 'What we found instead was no association at all, and even a suggestion of some protective effect.'
Federal health and drug enforcement officials have widely used Tashkin's previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought. "