Smoking cannabis and smoking tobacco can both harm the lungs, but they may cause different kinds of damage.
A study from the University of Otago in New Zealand found that long-term cannabis use was linked to changes in lung function that were not the same as those usually seen with tobacco.
The findings are important because cannabis use has become more common in many parts of the world. As laws change and cannabis becomes easier to obtain, researchers want to better understand what regular smoking may do to the body over many years.
The lungs bring oxygen into the body and remove carbon dioxide. Healthy lungs expand when we breathe in and then push air out again, but smoking can irritate and damage the airways and the delicate tissues involved in this process.
Professor Bob Hancox, one of the researchers, said long-term cannabis smoking was linked to lungs that held more air than normal. Cannabis users also showed greater resistance to airflow, meaning air did not move through their lungs as easily.
The researchers also found evidence that cannabis use may reduce the lungs’ ability to transfer oxygen into the blood. This type of problem has traditionally been strongly associated with tobacco smoking, making the cannabis finding particularly important.
The study used information from the Dunedin Multidisciplinary Health and Development Study, a long-running research project in New Zealand. It has followed more than 1,000 people who were born in Dunedin in 1972 and 1973.
Researchers have regularly collected information about the participants’ health and lifestyles as they have grown older. For this research, they were able to examine cannabis use and lung function up to age 45, providing a rare look at the possible effects of cannabis over several decades.
About three-quarters of the participants reported using cannabis at least once. Studying its long-term health effects has historically been difficult because cannabis was illegal in many countries and relatively few large studies collected detailed information about its use.
Doctors have previously reported severe lung damage in some people who smoke large amounts of cannabis. One condition sometimes informally called “bong lung” involves serious damage to lung tissue and has been associated with heavy cannabis smoking.
The researchers said some of the lung changes found in their study could possibly represent early signs of the type of damage seen in these heavy users. However, the study does not mean that everyone who has smoked cannabis will develop severe lung disease.
Tobacco smoking remains a well-established cause of lung cancer, emphysema and other serious diseases. The new findings do not suggest that cannabis is more dangerous than tobacco overall, but rather that the two substances appear to affect the lungs differently.
This may be especially important for people who smoke both cannabis and tobacco. Instead of one substance cancelling out the effects of the other, users could potentially experience different types of lung damage at the same time.
Scientists still do not fully understand why cannabis smoke produces a different pattern of lung changes. Differences in the substances being burned, the amount of smoke inhaled and the way people smoke cannabis may all play a role.
The study adds to evidence that inhaling cannabis smoke should not be considered harmless simply because cannabis comes from a plant. As cannabis becomes more widely available, understanding its long-term effects will be increasingly important for doctors, patients and public health officials.
The research was published in the American Journal of Respiratory and Critical Care Medicine.
Copyright © 2026 Knowridge Science Report. All rights reserved.
