Subjects who regularly inhale cannabis smoke possess no greater risk of contracting lung cancer than do those who consume it occasionally or not at all, according to data published online ahead of print in the International Journal of Cancer.

An international team of investigators from Canada, New Zealand, the United Kingdom, and the United States analyzed data from six case-control studies involving over 5,000 subjects (2,159 cases and 2,985 controls) from around the world.

Authors concluded, “Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers.”

Investigators had previously presented their data at the 2013 annual meeting of the American Academy for Cancer Research.

Their findings are similar to those of a 2013 review published in the journal Annals of the American Thoracic Society, which concluded: “[H]abitual use of marijuana alone does not appear to lead to significant abnormalities in lung function. … Overall, the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking.”

An accompanying commentary in the same journal affirmed, “[C]annabis smoking does not seem to increase risk of chronic obstructive pulmonary disease (COPD) or airway cancers. In fact, there is even a suggestion that at low doses cannabis may be protective for both conditions.”

Preclinical studies have documented that cannabinoids possess potent anti-cancer properties, including the inhibition of lung cancer cell growth. To date, however, scientists have yet to conduct controlled clinical trials replicating these results in human subjects.

The abstract of the study, “Cannabis smoking and lung cancer risk: Pooled analysis in the International Lung Cancer Consortium,” appears online here.

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