Short-term exposure may cause health effects such as eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath

Some people continue to maintain that second-hand cannabis smoke (SHCS) poses no risk, but a new study out of the U.S. begs to differ.

New York State’s Department of Health reports that particles in the PM2.5 size range “are able to travel deeply into the respiratory tract, reaching the lungs.”

This exposure can cause short-term health effects such as eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath, the information notes. That said, studies also suggest that long-term exposure “may be associated with increased rates of chronic bronchitis, reduced lung function and increased mortality from lung cancer and heart disease,” it adds.

Authors of the current study and research letter, published this week on JAMA Network Open, write that their findings “suggest SHCS in the home is not safe and that public perceptions of SHCS safety must be addressed.”

About a quarter of people think that SHCS is safe

More than one in four young people, 27 per cent, believe SHCS exposure is safe, note investigators. Indeed, an online survey of U.S. adults in 2017 found that about 18 per cent of respondents believe exposure to SHCS “is somewhat or completely safe for adults, whereas 7.6 per cent indicated that it is somewhat or completely safe for children,” report findings in Annals of Internal Medicine.

“Americans’ view of marijuana use is more favourable than existing evidence supports,” authors of that study wrote at the time.

With regard to the latest research, the favourable view is despite cannabis smoke containing “several hundred toxic chemicals, carcinogens and PM2.5,” many of which are at higher concentrations than tobacco smoke, authors report.

What are the dangers of second-hand smoke?

Second-hand tobacco smoke (SHTS) research to date has shown “causal links to cancer, respiratory and vascular disease, preterm birth and decreased immune function,” they write, citing a 2006 report from the Centers for Disease Control and Prevention.

That said, the same sort of concerns seems not to have attached themselves to cannabis smoking. Investigators report, however, that, like SHTS, one minute of “SHCS caused significant endothelial dysfunction in rats.”

According to Cedars Sinai, the endothelium is a thin membrane that lines the inside of the heart and blood vessels. These cells “release substances that control vascular relaxation and contraction as well as enzymes that control blood clotting, immune function and platelet adhesion,” the information explains.

Endothelial dysfunction “has been shown to be of significance in predicting stroke and heart attacks due to the inability of the arteries to dilate fully,” it adds.

Study believed to be a first

To explore SHCS exposure, the latest study measured PM2.5 levels as part of what investigators believe is the first research to “quantify SHCS levels from social cannabis smoking in the home.”

Using an aerosol monitor, measurements were taken before, during and after eight cannabis social-smoking sessions in a 20 metre-squared living room. The PM2.5 concentrations where a non-smoker might sit were measured.

Investigators report that bong smoking increased PM2.5 from background levels, conditions before the smoking began, by 100-fold to 1,000-fold for six of the eight test sessions. For the remaining two sessions, background levels were high and PM2.5 was more than 20-fold.

The mean PM2.5 concentrations increased in line with the time spent smoking, with the individual sessions lasting about one and a half to two hours. For two-hour smoking sessions, the mean, five-minute peak concentration remained at half strength 90 minutes after smoking had stopped.

“Each half-hour after smoking ceased, mean concentration declined to 78 per cent of peak value, then 60 per cent, then 40 per cent and after 110 minutes, 31 per cent,” the investigators report.

And not only did the fine particulate stick around, levels after bong smoking were greater than for either cigarettes or tobacco hookah (waterpipe) smoking. Indeed, cannabis bong smoking in the home generated four times greater PM2.5 concentrations than the other two.

Fine particulate concentrations higher than EPA daily standard

“If one assumes the exposure concentrations were at the mean levels observed, a single home smoking session with no other exposures would generate an estimated mean daily concentration that greatly exceeds the average in cigarette-smoking homes, non-smoking homes and the U.S. EPA (Environmental Protection Agency) daily standard,” study authors point out.

They write that while one of the study’s strengths was that measurements were taken in a real-world environment without artificial constraints, one of its limitations was that weed smoking was not directly observed. Investigators suggest more study is needed before drawing conclusions.

Per USA Today, lead author Patton Nguyen, an industrial hygienist and a graduate of the University of California, Berkeley School of Public Health, said there’s a discrepancy in the public view of SHCS and SHTS.

“There’s negative attitudes to second-hand tobacco smoke, but not really to second-hand cannabis smoke,” the publication quotes Nguyen as noting.

“What we want this study to do is really elucidate and help people understand that there are public health concerns,” he emphasized.

SHCS may pose a risk for children

Because some level of the particulate remains in the environment for hours following a bong sesh, “it can actually affect the health of children who are nearby or other people in pretty serious ways,” contended Katharine Hammond, a professor at U.C. Berkeley School of Public Health and corresponding author.

“We need to wake up to that,” Hammond said, per USA Today.

Information from the National Institute on Drug Abuse notes that “toxins and tar levels known to be present in marijuana smoke raise concerns about exposure among vulnerable populations, such as children and people with asthma.”

A study published in the spring of 2021 found that adults in U.S. states that have legalized cannabis and who also have children living at home more commonly use weed compared to states with no legal use. That may mean control and harm reduction efforts involving parents may need tweaking.

More generally, newly released Canadian research estimates about 17 per cent of people living in detached single-family homes and multi-unit housing in 2019 were exposed to SHCS.

In an email response to UPI regarding the new study, Hammond noted: “Bong smoking leads to extremely high and very unhealthy second-hand smoke particle concentrations.”

Researchers argue in the study “incorrect beliefs about SHCS safety promote indoor cannabis smoking.” The findings “suggest SHCS in the home is not safe and that public perceptions of SHCS safety must be addressed.”