Many Americans wrongly believe exposure to marijuana smoke is safer than tobacco, study finds
(CNN) -- Is inhaling marijuana smoke safer than inhaling smoke from tobacco? A majority of American adults say yes, according to a new survey, and they also believe there is less harm to adults and children from secondhand marijuana smoke than tobacco smoke.
However, those beliefs are just not true, said lead study author Dr. Beth Cohen, professor of medicine at the University of California, San Francisco and co-director of UCSF's program in residency investigation methods and epidemiology.
"When you burn something, whether it is tobacco or cannabis, it creates toxic compounds, carcinogens, and particulate matter that are harmful to health," she said in an email. "It's the combustion that's the problem, so this idea that because cannabis is 'natural' burning and inhaling it is fine is just wrong."
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While many longitudinal studies on the health impact of inhaling marijuana are still underway, there are "plenty of toxins and tar" in cannabis smoke that can hurt the lungs, said Carol Boyd, founding director of the Center for the Study of Drugs, Alcohol, Smoking and Health at the University of Michigan in Ann Arbor. She was not involved in the new study.
"I do not believe that comparing the health risks of marijuana smoking and tobacco smoking is useful any more than asking, 'Are eating cookies healthier than eating cake?' All smoke is an irritant to the respiratory tract and at a time in human history when humans breathe polluted air, NO added smoke is good," Boyd wrote in an email.
A growing acceptance
The study, published in the journal JAMA Network Open, surveyed over 5,000 people with an average age of 50 about their attitudes toward the safety of smoking weed versus smoking tobacco. They were also quizzed on whether they considered second-hand smoke from weed or tobacco to be potentially dangerous.
Conducted three times — in 2017, 2020 and 2021 — the surveys showed that people's positive perception of marijuana was increasing. By 2021, the last year of the survey, over 44% of the those surveyed thought cannabis was somewhat or much safer, compared with 25.5% who thought cigarettes were safer.
When it came to potential harm to others who might breathe marijuana smoke, over 40% thought smoke from weed was safer, compared with 23% who picked tobacco.
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"I cannot speak to the danger, but if a person is in a closed space with marijuana smokers, they can test positive for cannabis in their urine. They can also get some of the other physical effects of marijuana, including an increased heart rate and feeling 'high,' " Boyd said.
While study results on the health impacts of cannabis are increasingly concerning "our perceptions are going in the opposite direction," Cohen said.
"Though tobacco policies are becoming more restrictive, with bans on smoking in public places and on flavored products, cannabis is becoming increasingly available," she said. "There are also efforts to allow smoking of cannabis in places where smoking of tobacco is banned."
Concerning research
Research on the impact of cannabis on health is in its infancy. Historically it has been difficult to study cannabis use because weed has been illegal — and still is — in many states. In addition, the federal government historically had very strict regulations on how marijuana could be studied.
That began to ease, and with the legalization of cannabis for recreational use in many states, more researchers are now exploring the consequences of the habitual use of weed.
"What is generally known is that frequent smoking of marijuana is associated with chronic bronchitis, throat and bronchial inflammation," Boyd said. "While marijuana smoke contains carcinogens, such as benzoprene and benzanthracene, it does not appear that smoking marijuana causes lung cancer."
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A 2021 study found people who only smoked marijuana had higher blood and urine levels of several smoke-related toxins than nonsmokers. Those toxins are linked to anemia, liver and neurological damage, cancer and other health issues.
Another 2021 study found teens are about twice as likely to report "wheezing or whistling" in the chest after vaping marijuana than after smoking cigarettes or using e-cigarettes. In fact, regular cannabis vaping was associated with even more negative respiratory symptoms: disturbed sleep due to wheezing; limited speech due to wheezing; wheezing during or after exercise and experiencing a dry cough at night that was not due to a cold or chest infection.
A 2022 study looked at the lungs of people much younger than 50 who smoked both tobacco and cannabis and found 75% had emphysema, a disease of the small airways that causes damage to the air sacs in the lungs. About 67% of the tobacco-only smokers had emphysema, while only 5% of the nonsmokers had the disease, the study found.
"These patients presumably had less lifetime exposure to smoke, except they're even sicker than those who are heavy tobacco smokers and have been doing it longer," lead study author Dr. Giselle Revah, an assistant professor in the department of radiology at the University of Ottawa in Ontario, told CNN in a prior interview.
"We just don't know if it's a synergistic effect between the marijuana and the tobacco versus the marijuana alone," Revah said.
Another concern — marijuana users tend to inhale deeper and hold the smoke in their lungs longer, "which leads to a greater exposure per breath to tar," according to the American Lung Association.
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"Smoking marijuana hurts the lungs' first line of defense against infection by killing cells that help remove dust and germs as well as causing more mucus to be formed," the association said on its website.
Smoking marijuana also suppresses the immune system, the ALA said, and can leave users exposed to a mold that can grow on marijuana.
Although more research needs to be done on the impact on the lungs of people who smoke weed or the health effect of secondhand cannabis smoke, what is known is concerning, Cohen said.
"I am not anti-cannabis, I just want people to make informed decisions," she said. "Even if we do more research and find out that cannabis smoke is less harmful than tobacco smoke, that still doesn't mean it's safe."