Study: Smoking Marijuana Regularly Not Linked To Lung Cancer
By Steve Elliott
Regular marijuana smokers are no more likely to develop lung cancer than those who smoke only occasionally, according to a new study. The study's results back up those of other large-scale studies.
The finding of no significant increase in lung cancer risk held true whether marijuana users smoked once, twice, or more each day, and regardless of how many years they had smoked, Dr. Li Rita Zhang reported at the annual meeting of the American Association of Cancer Research, writes Michele G. Sullivan of the Oncology Report Digital Network.
The study incorporated data from six case-control studies from 1999 to 2012 in the United States, Canada, the United Kingdom, and New Zealand, with 2,159 lung cancer cases and 2,985 controls. All of the studies involved were part of the International Lung Cancer Consortium (ILCCO), an international group of researchers who share comparable data from ongoing and recently completed lung cancer studies from various geographical areas and ethnicities.
Dr. Zhang, of UCLA, performed two analyses on the data. One compared all lung cancer cases and all controls, regardless of concurrent or past tobacco use. Then, to reduce confounding by tobacco, she restricted her analysis to those who had never smoked tobacco.
That group comprised 370 cancer cases and 1,358 controls. The models were also adjusted for age, sex, sociodemographic factors, and tobacco pack-years. Habitual use of marijuana was defined as one joint per day, per year.
When compared with marijuana smokers who also used tobacco, habitual pot smokers showed no significant increase in cancer risk.
Looking at marijuana smokers and excluding tobacco smokers, there were no significant differences in any of the comparisons, including habitual vs. nonhabitual marijuana use; number of joints smoked per day; duration of up to 20 years or duration of more than 20 years.
"The conventional wisdom is that cannabis smoking is not as dangerous as cigarette smoking," said pulmonologist Michael Alberts.
The difference in risk could be at least partially related to chemical additives in commercial cigarettes that aren't present in marijuana smoke. But another major factor is almost certainly the fact that marijuana can slow or reverse cancer tumor growth, according to multiple studies.
For patients using medical marijuana, the benefits of smoking can outweigh the risks, according to Dr. Alberts, who is chief medical officer of the Moffitt Cancer Center in Tampa.
"You can think of it as similar to a CT scan," Alberts said. "Radiation isn't good, but if the scan is something beneficial and the risk is low, you take it. If cannabis is indicated, and if it's legal, and if there's literature backing up the indication for use, then you weigh the risk of smoking and the benefit it could bring, and make the decision."
(Graphic: Weed Smokers Guide)