Why Marijuana Doesn't Increase Your Lung Cancer Risk

It’s common knowledge that tobacco use can lead to lung cancer. Yet when it comes to marijuana, many people are still unsure.

In a recent study, researchers from Canada, the United States and New Zealand pooled data from six previous studies to determine whether smoking marijuana was associated with lung cancer.

The analysis was the largest of its kind, spanning more than 2,000 lung cancer cases and nearly 3,000 controls. Published June 20 in the International Journal of Cancer, the study found no link between marijuana use and lung cancer risk.

“Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers,” concluded the team, which included members from the International Lung Cancer Consortium.

Even when data was analyzed based on intensity, duration, consumption and age of initiation, no significant association was found.

The findings, the group adds, are consistent with a 2006 review that also showed no link between marijuana and lung cancer after adjusting for tobacco use.

Not Enough Exposure

Despite the fact that marijuana users don’t appear to be at greater risk of lung cancer, marijuana smoke has been shown to contain carcinogens. In fact, studies show a marijuana ‘joint’ deposits four times as much tar in the lungs than an equivalent tobacco cigarette.

Hal Morgenstern, PhD, a University of Michigan epidemiologist and co-author of the latest study, suggests it might be that most marijuana users don’t smoke enough of it to get sick.

“When you think about people smoking 20-40 cigarettes a day for 40 years, they’re smoking hundreds of thousands of cigarettes. The exposure that marijuana users get… is more than a magnitude of difference less.”

On the other hand, cannabis smokers are known to inhale deeper and hold smoke in their lungs for longer than cigarette smokers do.

THC May Protect

Others who have studied the link between marijuana and lung cancer point to an often overlooked difference between marijuana and tobacco — certain compounds in marijuana have been shown to have anti-cancer effects.

This may be the reason why marijuana smokers are unlikely to develop lung cancer, explains Donald P. Tashkin, MD, a lung specialist from the University of California.

“The THC in marijuana has well-defined anti-tumoral effects that have been shown to inhibit the growth of a variety of cancers in animal models and tissue culture systems, thus counteracting the potentially tumorigenic effects of the procarcinogens in marijuana smoke.”

In fact, published in 2006, one of Dr. Tashkin’s own studies found that while heavy tobacco smokers experienced up to a 20-fold increase in lung cancer risk, the most frequent users of cannabis were no more likely to develop lung cancer than the average person.