If you ever find yourself coughing up a lung, so to speak, it might be because of all that weed you’ve been smoking.
A new study from respiratory experts in New Zealand says that available evidence indicates that smoking cannabis causes bronchitis and is associated with changes in lung function.
But whereas inhaling cannabis smoke appears to increase the risk of severe bronchitis at low exposure, there’s no convincing evidence that it leads to chronic obstructive pulmonary disease (COPD), a condition caused by long-term tobacco use. People with COPD are at a high-risk for developing heart disease and lung cancer.
Bronchitis is an inflammation of the lining of your bronchial tubes, which carry air to and from your lungs.
Cannabis use, according to the study published in the journal Addiction, is associated with increased central airway resistance, lung hyperinflation and higher vital capacity with little evidence of airflow obstruction or impairment of gas transfer.
“These changes are most likely to be a consequence of bronchitis, although this is not proven,” says author and research professor Bob Hancox. “The bronchitis changes in the central airways are likely to increase resistance — people may notice this as increased difficulty breathing, but will probably notice the bronchitis symptoms of cough, sputum production, and wheeze even more.”
The hyperinflation and higher vital capacity may be part of a compensatory mechanism due to the bronchitis, he says. It’s also been suggested that this is because of the way people smoke it: taking a big breath in and holding it. But no one knows for sure.
Hancox is a respiratory specialist at the University of Otago who investigates why people develop diseases like asthma, allergies, and chronic lung disease. Much of his research is based on the famous, long-running Dunedin Multidisciplinary Health and Development Study, which has followed 1,037 children since their birth in Dunedin, New Zealand in the early 1970s into adult life. The longitudinal study covers topics from the outcomes of stress to long-term cannabis use.
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There’s a strong association between using cannabis and bronchitis symptoms, Hancox says.
“In our earlier research, we found that about a third of people who used cannabis once a week or more had symptoms of bronchitis — about 3 times higher than non-users,” he says.
Hancox notes that he’s seen other research that suggests the airway changes related to bronchitis in people who smoke only a few joints a day are similar to that seen in people who smoke 20-30 tobacco cigarettes a day.
Data from other leading researchers on cannabis and lung health, like Dr. Donald Tashkin of UCLA, corroborate that weed smoke causes bronchitis symptoms but suggest that they subside after ceasing use. Pashkin’s research also shows that inhaling cannabis smoke is generally less risky than tobacco.
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Global research on cannabis and the lungs has been limited by its legal status, the variability in strength and size of cannabis cigarettes, and the fact that most cannabis users also smoke tobacco — making the effects difficult to separate, the New Zealand study says.
Some studies suggest there’s a link between smoking weed and lung cancer. Other studies have not found this.
“We need more evidence,” Hancox says.
According to data from the U.S. Center for Disease Control, lung cancer kills upwards of 127,000 Americans per year and is the leading cause of death among tobacco smokers.
Top image by Sonya Yruel via Drug Policy Alliance