Does Marijuana Cause Lung Cancer?

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Lung cancer and marijuana links still unclear

September 21, 2013 / Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

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(dailyRx News) Scientists have long been debating whether or not marijuana can be linked to lung cancer. A 40-year review suggests that cannibis (marijuana) does increase lung cancer risks, but the study is flawed, according to a leading cancer expert.
A new long-term study looked at the risk of lung cancer among young marijuana users.

The researchers concluded that heavy marijuana use may indeed elevate the risk of lung cancer.

But one of the nation’s leading lung cancer experts, D. Ross Camidge, MD, PhD, blows smoke on this study’s findings.

"Consider the risks of anything you inhale into your lungs."

Russell C. Callaghan, PhD, associate professor at University of Northern British Columbia in Prince George, led this study.

“Tobacco smoking is the major cause of lung cancer, and marijuana and tobacco smoke contain many of the same potent carcinogens,” the authors wrote.

For this population-based study, the researchers examined data on 49,321 men between the ages of 18 and 20 who were being enlisted in the Swedish military between 1969 and 1970.

These participants completed surveys on a number of health and lifestyle issues, including their lifetime use of marijuana.

Those who responded that they had used cannabis more than 50 times were considered "heavy" users.

Initial surveys found that 10.5 percent of the study members had used cannabis, and 1.7 percent were considered heavy users.

The surveys also asked participants about their tobacco smoking and alcohol use, along with any history of respiratory problems and their socioeconomic status.

The researchers tracked the study members for the development of lung cancer through 2009.

A total of 189 cases of lung cancer were diagnosed among the original group.

The researchers found that lung cancer risks were more than two times (212 percent) greater in those who were initially categorized as heavy marijuana users compared to never users. This increased risk stood even after adjusting for baseline (initial) tobacco and alcohol use, respiratory conditions and socioeconomic status.

“Our findings do raise concern about the potential long-term lung cancer risk associated with marijuana use in adolescence and young adulthood — a time of pronounced lung development — especially given the possibility that such marijuana smoking may occur during a ‘critical period’ of lung cancer susceptibility to carcinogens in marijuana smoke,” the authors concluded.

Dr. Ross Camidge, who is associate professor of medicine/oncology and director of the Thoracic Oncology Clinical Program at the University of Colorado Cancer Center, told dailyRx News, “Whether marijuana is associated with cancer risk continues to be debated. We know smoking risk is adjusted by number and duration of cigarette smoking.”

He continued, “In this study they only had a snapshot of smoking use to adjust the snapshot of cannabis use by. Therefore it is impossible to deduce a causative role and not an associative one (cannabis may be associated with longer duration of smoking in a lifetime, for example)."

Dr. Camidge, who was not involved in this study, added, “Also, there are many ways to use cannabis other than smoking and this doesn't allow for that distinction to occur.”

Incidentally, the latest Gallup poll suggests that fewer young people are using marijuana. From a high (no pun intended) of 56 percent of 18- to 29-year-olds saying they had tried cannabis (marijuana) in 1977 and 1985, only 36 percent of that age group reported smoking weed in 2013.

This study was published in the October issue of Cancer Causes & Control.

This research was supported by the Ontario Ministry of Health and Long-Term Care. No conflicts of interest were reported.