Marijuana might do more damage to smokers than cigarettes alone.
A study published Tuesday in the journal Radiology demonstrated higher rates of conditions including emphysema and airway inflammation among people who smoke marijuana than among nonsmokers and people who smoked only tobacco. Nearly half of the 56 marijuana smokers whose chest scans were reviewed for the study had mucus plugging their airways, a condition that was less common among the other 90 participants who didn’t smoke marijuana.
“There is a public perception that marijuana is safe and people think that it’s safer than cigarettes,” said Giselle Revah, a radiologist who helped conduct the study at the Ottawa Hospital in Ontario. “This study raises concerns that might not be true.”
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One-fifth of Canadians over 15 years old reported using marijuana in the past three months, according to a 2020 survey of some 16,000 people conducted by Canada’s national statistical office. About 18% of Americans reported using marijuana at least once in 2020 in the U.S. Substance Abuse and Mental Health Services Administration’s National Survey of Drug Use and Health, including about one in three young adults age 18 to 25. The surveys didn’t ask how marijuana was consumed. About one-fourth of people over 12 years old believed there was great harm from smoking marijuana once or twice a week, according to the survey.
Previous studies have found that marijuana is more likely than tobacco to be smoked unfiltered and that smokers tend to inhale more smoke and hold it in their lungs longer. Bong smoke contains tiny pollutants that can linger indoors for up to 12 hours, a study published in March in JAMA Network Open showed.
Among the 56 marijuana smokers in the Ottawa study, 50 also smoked tobacco. The tobacco-only smokers were patients whose chest scans were performed as part of a high-risk lung-cancer screening program that included people age 50 and above who had smoked for several years.
Marijuana’s illicit status long discouraged substantial research into the long-term effects of its use, said Albert Rizzo, chief medical officer for the American Lung Association, who wasn’t involved in the study. Inhaling any heated substance can irritate airways, among other health dangers, he said.
“There could be an additive effect if you smoke cigarettes as well as marijuana,” Dr. Rizzo said.
The study authors found bronchial thickening in 64% of marijuana smokers versus 42% of tobacco-only smokers and a condition that leads to excess mucus buildup in 23% of marijuana smokers versus 6% of tobacco-only smokers.
Age-matched marijuana smokers had higher rates of emphysema (93%) than tobacco-only smokers (67%), and the emphysema, which appears in imaging as small holes in lung tissue, was more prevalent in the marijuana smokers, the study found.
Write to Julie Wernau at julie.wernau@wsj.com
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