Smoking marijuana might not cause lung cancer…and could even fight it

In Cancer, Feature Stories, Research Updates and News by Dr. Tim Sandle, Ph.D.

A new research study indicates that smoking marijuana in low or medium quantities is unlikely to cause lung cancer. This means that medical cannabis smoking is probably considerably safer than puffing away at tobacco.

The finding comes from a new study conducted by Professor Donald P. Tashkin, emeritus professor of medicine at UCLA’s David Geffen School of Medicine. Professor Tashkin, who is also the Medical Director of the Pulmonary Function Laboratory, has been studying marijuana and its effects on the lungs for over 30 years.

The study reveals that light to moderate marijuana use does not cause increased lung cancer risk, while there is insufficient data to show whether heavy use of marijuana presents a cancer risk. This finding comes despite marijuana smoke containing many of the same carcinogens as tobacco smoke.

When asked what constitutes “heavy use,” Tashkin suggested it applies to those “who had smoked more than 22,000 joints over a lifetime,” while “moderate use applies to those who “had smoked between 11,000 to 22,000 joints.”

Tashkin’s study was based on a review of various published studies, and was a follow-up to a review he carried out in 2006. He concludes that these “findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use.”

In relation to regular marijuana users, the professor went on to say that “if they smoke a small or moderate amount there is no increased risk; in fact a slightly less one.”

The reason that marijuana seemingly does not induce cancer, whereas tobacco does, is linked to the chemicals found in marijuana – specifically tetrahydrocannabinol, or THC, which is a chemical found in marijuana smoke.

It is Tashkin’s view that “cellular studies and even some studies in animal models suggest that THC has antitumor properties, either by encouraging the death of genetically damaged cells that can become cancerous or by restricting the development of the blood supply that feeds tumors.”

Another reason that could explain the findings is that “marijuana is packed more loosely than tobacco, so there’s less filtration through the rod of the cigarette, so more particles will be inhaled. It’s noticeable that marijuana smokers typically smoke differently than tobacco smokers. They hold their breath about four times longer, allowing more time for extra fine particles to deposit in the lung.” Thus the beneficial properties found in THC can make their way into the body.

To show that other factors were not influencing the results, Tashkin took into account smokers’ regular use of tobacco and alcohol, other types of drugs, their diet, occupation, family history of cancer and socioeconomic status, as well as their marijuana use. These different factors were “normalized” so that the marijuana vs. tobacco differences could be seen.

The research does not indicate that smoking marijuana (or any substance) is entirely safe. Smoking marijuana, as with tobacco, presents a risk of bronchitis, although even here its effects on the lungs are less when compared with tobacco smoking.

Nonetheless, the news has been well received by medical marijuana users. One smoker, U.K. resident David Porter, said, “I’ve been smoking cannabis for several years for MS. I’ve found this to be the best way to take it…the effect is really quick and the pain is reduced quickly.

“Naturally, I’ve been concerned for a long time about the risks of smoking. I haven’t smoked tobacco for several years, not since the 1990s due to the cancer risks. Although I probably would have carried on smoking cannabis for my condition, hearing news like this makes the situation a lot better for me.”

Commenting on Tashkin’s recent work, Dr. Mark Ware said that the study had presented “the most comprehensive and authoritative review of the subject ever published” and that “cannabis smoking is not the same as tobacco smoking in terms of respiratory risk.”

Professor Tashkin’s study has been published in the distinguished journal Annals of the American Thoracic Society (June 2013).

A study on bladder cancer issued around the same time found a similar pattern, in that incidents of bladder cancer are considerably lower in smokers of marijuana compared with cigarette smokers. This finding is based on a study carried out by Kaiser Permanente researchers, led by Dr. Anil A. Thomas.