source: https://www.sacbee.com/livinghere/story/1861861.html UCLA's Tashkin studied heavy marijuana smokers to determine whether the use led to increased risk of lung cancer and chronic obstructive pulmonary disease, or COPD. He had hypothesized that there would be a definitive link between cancer and marijuana smoking, yet the results proved otherwise. "What we found instead was no association and even a suggestion of some protective effect," says Tashkin, whose research was the largest case-control study ever conducted. The study was funded by the National Institutes of Health. Tobacco smokers in the study had as much as a 21-fold increase in lung cancer risk. Cigarette smokers, too, developed COPD more often in the study, and researchers found that marijuana did not impair lung function. Tashkin, supported by other research, concluded that the active ingredient tetrahydrocannabinol, or THC, has an "anti- tumoral effect" in which "cells die earlier before they age enough to develop mutations that might lead to lung cancer." However, the smoke from marijuana did swell the airways and lead to a greater risk of chronic bronchitis. "Early on, when our research appeared as if there would be a negative impact on lung health, I was opposed to legalization because I thought it would lead to increased use and that would lead to increased health effects," Tashkin says. "But at this point, I'd be in favor of legalization. I wouldn't encourage anybody to smoke any substances, because of the potential for harm. But I don't think it should be stigmatized as an illegal substance. "Tobacco smoking causes far more harm. And in terms of an intoxicant, alcohol causes far more harm."