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Smoking marijuana can raise risk of lung disease, chest scans indicate

In a new analysis of medical records, cannabis smokers had higher rates of a certain type of emphysema than tobacco smokers.
An activist smokes marijuana during the annual NYC Cannabis Parade & Rally in support of the legalization of marijuana for recreational and medical use, in N.Y., on May 1, 2021.
A marijuana smoker in New York in May 2021.Angela Weiss / AFP via Getty Images file

Smoking marijuana could be more harmful than people realize, a new study suggests.

Chest scans show marijuana smokers may be more likely to develop inflamed airways and a certain type of emphysema than people who puff away on traditional cigarettes.

The analysis by Canadian researchers, published Tuesday in Radiology, compared the chest scans of marijuana smokers and tobacco-only smokers who were matched according to age. They found that twice as many of those who inhaled cannabinoids developed paraseptal emphysema as people who smoked cigarettes only.

Paraseptal emphysema is a disease of the small air sacs of the lungs that are responsible for taking in oxygen and removing carbon dioxide, said a study coauthor, Dr. Giselle Revah, a cardiothoracic radiologist at The Ottawa Hospital.

“When they are damaged, small holes are created in the lungs and gas exchange doesn’t work as well,” she said.

The higher rate of paraseptal emphysema among marijuana smokers could be due to two factors, Revah suspects. Unlike cigarettes, joints aren’t filtered, and marijuana smokers inhale more deeply and longer than cigarette smokers do.

While it isn’t as lethal as the most common type of emphysema linked with long-term heavy tobacco smoking, paraseptal emphysema can lead to a number of distressing symptoms, said a pulmonologist and longtime cannabis researcher, Dr. Donald Tashkin of the UCLA David Geffen School of Medicine.

Emphysema symptoms include: 

  •  Shortness of breath climbing stairs.
  • A sensation that a person can’t get enough air in the lungs.
  • Persistent cough and wheezing.
  • Coughing up mucus.
  • Fatigue.

Paraseptal emphysema can sometimes lead to a collapsed lung, which can be life-threatening, Tashkin said.

No form of emphysema is curable.

To take a closer look at the impact of smoking marijuana on lung health, Revah and her colleagues reviewed the medical records of 146 patients who had received a special kind of X-ray called a CT scan.

The marijuana smokers were identified by a search through the Ottawa Hospital records, using the terms “marijuana” and “cannabis.” Then Revah and her colleagues determined which of the marijuana smokers had had the chest scan.

They then searched for nonsmokers and the cigarette smokers who had received chest scans to compare to the marijuana smokers. 

“The lungs were not designed for cigarette or marijuana smoke.”

Dr. Panagis Galiatsatos, Johns Hopkins

Among the 56 who reported smoking marijuana, 28 provided information about the amount, which was 1.85 grams per day on average. Most of the marijuana smokers, 50 of 56, said they also smoked tobacco.

The marijuana smokers were ages 20 to 73, the nonsmokers were ages 19 to 75, and the tobacco-only smokers were ages 50 to 71.

Overall, 75% of marijuana smokers in the analysis were found to have some type of emphysema, compared with 5% of nonsmokers and 67% of tobacco-only smokers. When the researchers focused on patients from the three groups who were age 60 on average (30 marijuana smokers, 33 tobacco-only smokers and 29 nonsmokers) they found that 57% of the marijuana smokers had paraseptal emphysema, compared with 24% of the tobacco-only smokers.

The marijuana smokers also had higher rates of airway inflammation.

The findings didn’t surprise Dr. Panagis Galiatsatos, a pulmonologist who is the director of the Tobacco Treatment Clinic at Johns Hopkins Medicine.

“Chemicals’ and toxins’ going to the lungs on a regular basis will result in damage,” Galiatsatos said. “The lungs were not designed for cigarette or marijuana smoke.”

More news on cannabis

The research has limitations, including its small size, so it needs to be validated with a larger study, Galiatsatos said.

People should understand “that all inhalation is bad for the lungs, whether it is tobacco smoke or marijuana smoke,” said Dr. Thomas McLaren, a cardiothoracic radiologist who is an assistant professor of radiology and cardiology at Vanderbilt University Medical Center.

If you’re going to use cannabis, “this is absolutely not the best way to do it, McLaren said, adding that edibles are what is suggested for cancer patients.

A previous UCLA study of people who smoke only marijuana found symptoms of chronic bronchitis and widespread pathological changes in the airways, Tashkin said.

“So smoking marijuana is doing some injury to the central airways,” he said.

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