Researchers at University of California San Diego analysed cannabis smoking practices in San Diego County to assess whether in-home smoking was associated with cannabis detection in children. The study, published in the January 23, 2025, online edition of the Journal of the American Medical Association Network Open, found that in-home cannabis smoking increased the odds of child exposure to cannabis smoke.

Smoking is the most common method of cannabis use and is known to generate emissions that are harmful to those exposed. Cannabis is often smoked indoors, putting non-smokers such as children at risk for exposure.

“While the long-term health consequences of cannabis smoke are not yet well known, cannabis smoke contains carcinogens, respiratory irritants, and other harmful chemicals,” said John Bellettiere, Ph.D., M.P.H., assistant professor in the Herbert Wertheim School of Public Health and Human Longevity Science at UC San Diego. “In our analysis, the odds of detectable cannabis in children were five times higher in households with reported in-home cannabis smoking. This exposure to toxic chemicals, including known carcinogens, could have long-term health effects in these children.”

The research team analysed in-home cannabis smoking practices in San Diego County to quantify the relationship between in-home cannabis smoking and cannabis biomarker detection in resident children’s urine. The youngest child in each of the 275 households enrolled in the study was tested, at a median age of three years.

Investigators found that among households reporting in-home cannabis smoking, 69% had a child with detectable cannabis biomarker levels compared to 24% in households not reporting in-home cannabis smoking. Because a large percentage of participants were recruited from low-income households enrolled in the Women, Infants, and Children Supplemental Nutrition Program from 2012 through 2015, the findings of the study are not necessarily generalisable to the broader U.S. population, cautioned Bellettiere.

“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,” said Osika Tripathi, Ph.D., M.P.H., a recent graduate of the UC San Diego – San Diego State University Joint Doctoral Program in Public Health.

“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,” continued Bellettiere. “Determining the long-term health risks of second-hand cannabis smoke exposure is the essential next step.”

The study was funded, in part, by the National Heart, Lung, and Blood Institute of the National Institutes of Health (grant # R01HL103684), the National Institutes of Health (grant #T32HL079891-11, grant #T32 GM084896), the Tobacco-Related Disease Research Program (awards # T31KT1501, #T33PC6863, #T32PT6244, #T32PT6042 and #T32IR5208), the National Cancer Institute (#K01 CA234317), the San Diego State University/ UC San Diego Comprehensive Cancer Center Partnership (#U54 CA132384 and #U54 CA132379), and the Alzheimer’s Disease Resource Center for Advancing Minority Aging Research at UC San Diego (#P30 AG059299).

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Disclosures: The authors declare no competing interests.