Cannabis is increasingly accessible in many countries, including several that have recently relaxed prohibition laws or legalized recreational use for adults.
Yet while cannabis has often been misleadingly vilified by critics supporting prohibition, smoking it may nonetheless pose legitimate health risks, and not necessarily just for those who choose to do so.
According to a new study, smoking cannabis inside a home is associated with a higher likelihood of cannabis biomarkers in the urine of children who live there.
There are caveats, the authors note, but this still highlights the potential harm, and suggests further study is warranted – along with precautions, like smoking outside, that might help parents and guardians reduce risk in the meantime.
“While the long-term health consequences of cannabis smoke are not yet well-known, cannabis smoke contains carcinogens, respiratory irritants, and other harmful chemicals,” says John Bellettiere, an epidemiologist at the University of California San Diego.
“In our analysis, the odds of detectable cannabis in children were five times higher in households with reported in-home cannabis smoking,” he says. “This exposure to toxic chemicals, including known carcinogens, could have long-term health effects in these children.”
Bellettiere and his colleagues studied in-home cannabis-smoking habits in San Diego County, California, using data from Project Fresh Air (PFA); a randomized clinical trial conducted in the county between 2012 and 2016 to reduce levels of fine particulate matter in homes.
PFA recruited participants through various sources, including community events and organizations such as the US Department of Agriculture’s Special Supplemental Nutrition Program for Women, Infants, and Children (WIC).
To be eligible for the project, participants needed to be at least 18 years old, have at least one child younger than 14 living in the home, have a resident adult tobacco smoker in the home, and have no plans to move within three months.
The final sample included 275 households, each of which had an air particle monitor installed by project staff in the room where most of the tobacco smoking took place. The monitors continuously counted fine aerial particles.
PFA staff also placed passive nicotine dosimeters within two feet of monitors.
After seven days, PFA staff interviewed each enrolled parent or guardian, asking about household characteristics as well as any particle-generating activities, like smoking or cooking, in the previous week.
Staff also gave each parent or guardian a urine-collection kit, along with instructions for collecting urine from the enrolled child. They tested the youngest child in each household, with a median age of 3 years.
Years later, portions of these urine samples were sent to a US Centers for Disease Control and Prevention lab for analysis of cannabis-exposure biomarkers, as part of a secondary cross-sectional study conducted in 2020, called Eliminating In-Home Smoking.
Using data from these sources in a new study, researchers found that 69 percent of households reporting in-home cannabis smoking had a child with detectable cannabis biomarker levels – compared with just 24 percent among households not reporting in-home cannabis smoking.
“As young children spend most of their time at home, reducing in-home cannabis smoking could substantially reduce their exposure to the toxic and carcinogenic chemicals found in cannabis smoke,” says Osika Tripathi, an epidemiologist at UC San Diego.
Research on cannabis lags half a century behind tobacco research due to “restrictive policies and regulations around cannabis research,” the authors note, and the long-term health effects of cannabis exposure remain murky. Yet there are reasons for concern, especially with regards to children.
“As evidence regarding the health effects of cannabis grows, adopting strategies from the tobacco-control playbook, such as comprehensive smoke-free laws and policies, could safeguard children’s health,” Bellettiere says.
The study has notable limitations, the researchers acknowledge. Participants could have underreported in-home cannabis smoking, especially since recreational cannabis use was not yet legal in California when the data were collected.
The original data collection focused more on tobacco than cannabis, and the sample was limited to households with an adult tobacco smoker.
The sample was also largely recruited from lower-income households enrolled in the WIC program, the researchers note. These factors mean the findings are not necessarily generalizable to the broader US population.
Effects of in-home cannabis smoking could also vary significantly by by method, location, and frequency of smoking, they point out. And previous tendencies to smoke indoors may have faded since 2016 due to more liberal regulations and social attitudes.
Still, given the potential stakes for kids at key developmental stages, this is worth looking into further, the researchers contend.
“Determining the long-term health risks of second-hand cannabis smoke exposure is the absolutely essential next step,” Bellettiere says.
The study was published in the Journal of the American Medical Association Network Open.
