Long-term cannabis smoking damages lungs differently than tobacco, study finds


Individuals who are regular and long-term cannabis smokers are at risk for lung damage, but the impact looks different than those who smoke tobacco, according to new research.

The study, published in the American Journal of Respiratory and Critical Care Medicine, was authored by researchers at the University of Otago in New Zealand, Duke University in North Carolina, and McMaster University in Ontario, Canada. The findings are part of the long-running Dunedin Multidisciplinary Health and Development Study.

Bob Hancox, MBChB, the study’s co-author and professor in the University of Otago’s Department of Preventive and Social Medicine, said prolonged cannabis use led to over-inflated lungs and increased the resistance to airflow to a greater extent than tobacco.

“It was also found that cannabis use may also impair the ability of the lungs to extract oxygen from the breath,” said Hancox. “This is a known consequence of smoking tobacco but has not been demonstrated with cannabis until now.”

Researchers sought to assess the effects of cannabis and tobacco on lung function in a cohort study comprised of 1,037 middle-aged adults. Cannabis and tobacco use were reported at various ages – 18, 21, 26, 32, 38 and 45 years. Spirometry, plethysmography, and carbon monoxide transfer factor were measured at age 45. Associations between lung function and cannabis use were adjusted for tobacco use, according to the study.

Some patients who smoke cannabis frequently have a distinct form of lung damage, according to researchers, which is classified as a very severe form of emphysema. The study’s findings concluded that over-inflated lungs, increased airway resistance, and impaired oxygen extraction, may reflect early signs of this disease.

The study’s results showed that cannabis use is associated with higher lung volumes suggesting hyperinflation. Increased large-airways resistance and lower mid-expiratory airflow was evident but impairment of forced expiratory volume in one second to forced vital capacity ratio was due to higher vital capacities. This pattern of effects is different to those of tobacco, according to the study.

The Dunedin Multidisciplinary Health and Development Study has documented cannabis use and measured lung function throughout adult life up to age 45 in more than 1,000 individuals born in Dunedin in 1972/73.

Integrative practitioners who prescribe medical marijuana can talk with their patients about alternative forms of cannabis consumption to smoking. In addition, if their patients are smoking cannabis habitually, recommending alternative ways to consume can be incorporated into their overall treatment plan.