4th February 2022
By Roland Sebestyén

While it has been known for a long time that both cannabis and tobacco use alter both lung function and capacity, researchers have now discovered the subtle differences in how the two substances impact a person’s breathing.

In a study recently published in the American Journal of Respiratory and Critical Care Medicine, researchers revealed that, while smoking both substances is associated with hyperinflation, there is evidence of increased large-airway resistance and lower mid-expiratory airflow in cannabis users.

However, cannabis smoking, eventually, could lead to gas trapping and impairment of Forced Expiratory Volume in one second to Forced Vital Capacity ratio is due to higher Vital Capacities.

Study co-author Professor Bob Hancox said: “Although the effects of cannabis were detrimental, the pattern of lung function changes was not the same.

The research found that 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. This is a known consequence of smoking tobacco, but has not been demonstrated with cannabis until now.”

The study included data from 881 (88%) of 997 surviving participants. Cannabis use was also associated with higher total lung capacity, functional residual capacity, residual volume, and alveolar volume along with lower mid-expiratory flows, airway conductance, and transfer factor.

Quitting regular cannabis use between assessments was not associated with changes in spirometry.

Professor Hancox added: “Although cannabis is one of the world’s most widely used drugs, there has been little research on the effects on the lungs. This is because it has been difficult to study a drug that remains illegal in most parts of the world.

“The latest Dunedin study findings support observations from other research that cannabis has different effects to tobacco. The Dunedin results extend these findings with more complete measures of cannabis use and a full assessment of lung function using eleven different measures.

“Of course, people who smoke both cannabis and tobacco are likely to suffer lung damage from both substances.”

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