“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. 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.” – Dr. Tashkin
THC has been found to reduce tumor growth in common lung cancer by 50 percent and to significantly reduce the ability of the cancer to spread, say researchers at Harvard University, who tested the chemical in both lab and mouse studies. The researchers suggest that THC might be used in a targeted fashion to treat lung cancer. (study)
Although the researchers do not know why THC inhibits tumor growth, they say the substance could be activating molecules that arrest the cell cycle. They speculate that THC may also interfere with angiogenesis and vascularization, which promotes cancer growth.
In 2006, Donald Tashkin, M.D., of the University of California in Los Angeles, presented the results of his study,”Marijuana Use and Lung Cancer: Results of a Case-Control Study”.
Tashkin found that smoking marijuana does not appear to increase the risk of lung cancer or head-and-neck malignancies, even among heavy users. The more tobacco a person smoked, the greater their risk of developing lung cancer and other cancers of the head and neck. But people who smoked more marijuana were not at increased risk compared with people who smoked less and people who didn’t smoke at all. Study
Even very heavy, long-term marijuana users who had smoked more than 22,000 joints over a lifetime seemed to have no greater risk than infrequent marijuana users or nonusers.
The findings surprised the study’s researchers, who expected to see an increase in cancer among people who smoked marijuana regularly in their youth.
“We know that there are as many or more carcinogens and co-carcinogens in marijuana smoke as in cigarettes,” researcher Donald Tashkin, MD, of UCLA’s David Geffen School of Medicine tells WebMD. “But we did not find any evidence for an increase in cancer risk for even heavy marijuana smoking.” Carcinogens are substances that cause cancer.
Marijuana use was associated with cancer risk ratios below 1.0, indicating that a history of pot smoking had no effect on the risk for respiratory cancers. In contrast, tobacco smoking had a 21-fold risk for cancer. Tashkin concluded, “It’s possible that tetrahydrocannabinol (THC) in marijuana smoke may encourage apoptosis, or programmed cell death, causing cells to die off before they have a chance to undergo malignant transformation”. Study
The new findings “were against our expectations,” said Donald Tashkin of the University of California at Los Angeles, a 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.”
Similar findings on the safety of smoked marijuana were released in April 2009 by the Vancouver Burden of Obstructive Lung Disease Research Group. The study presents that smoking both tobacco and marijuana synergistically increased the risk of respiratory symptoms and COPD. Smoking only marijuana, however, was not associated with an increased risk of respiratory symptoms of COPD. Study
In a related commentary, Dr. Donald Tashkin writes that “the findings — add to the limited evidence of an association between marijuana use and COPD because [the] study focuses on an older population (aged 40 or older) that is at greater risk of COPD.” revious studies have failed to find an additive effect of marijuana and tobacco on either chronic respiratory symptoms or abnormal lung function in younger smokers. Dr. Tashkin states that “we can be close to concluding that marijuana smoking by itself does not lead to COPD.””. Source
Here is Dr. Tashkin discussing the findings: