Detectable THC biomarkers among children via in-home, second-hand cannabis smoke | Image Credit: © TaylerDerden - ©TaylerDerden - stock.adobe.com.

Background

A reduction of in-home cannabis smoke could "substantially" reduce children's exposure to toxic and carcinogenic chemicals that are in smoke, according to newly-published research.

Cannabis smoking, the most common method of cannabis use, is known to generate emissions that are harmful to individuals exposed. Nonsmokers such as children, who spend most of childhood at home, can be exposed to the smoke, especially since cannabis use is on the rise among parents with children living in the home.

That's according to a study titled "Exposure to secondhand cannabis smoke among children," published today in JAMA Network Open. The study was led by Osika Tripathi, PhD, of the San Diego State University of Public Health.

"Cannabis smoking also emits large amounts of PM_2.5 (fine particulate matter with aerodynamic diameters 2.5 μm or below), which negatively impacts cardiovascular and pulmonary health and correlates with respiratory burden of carbon monoxide and insoluble particulates (tar)," wrote Tripathi and colleagues.

"Secondhand cannabis smoke (SHCS) is smoke either directly from burned cannabis or from smoker exhalations. SHCS exposure has only recently been objectively quantified through detection of small amounts of cannabinoids in the urine," stated the study investigators.

To determine the degree that in-home cannabis smoking can be detected in the urine of resident children, a cross-sectional study of 275 children was conducted to test the association of in-home cannabis smoking with urinary cannabinoids of children living at home.

Study details and results

Using data from Project Fresh Air, a randomized clinical trial to reduce fine particulate matter levels, eligible participants were recruited from San Diego County, California, households that included children under 14 years of age and an adult tobacco user. Urine samples from children in the study were analyzed in 2022.

In-home cannabis use was measured by a parent or guardian report of cannabis smoking, number of daily nonspecific smoking events computed via an air particle count algorithm; and number of daily cannabis smoking events ascertained by residualization, adjusting for air nicotine, tobacco smoking, and other air particle generating or ventilating activities.

Levels of the cannabis biomarker Δ⁹-tetrahydrocannabinol (THC) and its major metabolites, 11-hydroxy-Δ⁹-tetrahydrocannabinol and 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol were main measures. Biomarker molar equivalents were summed to represent total THC equivalents (TTE) in urine. Then, logistic regression assessed whether in-home smoking was associated with cannabis biomarker detection.

"For children with detectable urinary cannabinoids, linear regression assessed in-home smoking association with quantity of urinary TTE," wrote the study authors.

Analysis featured 275 children with a mean age of 3.6 years (52.4% males). In all, 29 households reported in-home smoking in the last week, with 75 children having detectible urinary cannabinoids.

In households with reported in-home smoking, odds of detectable TTE in children's urine were "significantly higher" compared to those without smoking (odds ratio [OR], 5.0; 95% CI, 2.4-10.4).

Odds also increased with each additional ascertained daily cannabis smoking event, according to study results (OR, 2.5; 95% CI, 1.6-3.9).

Conclusion

"In this cross-sectional study, in-home cannabis smoking was associated with significantly increased odds of child exposure to cannabis smoke, as assessed by urinary cannabinoid biomarkers," wrote the authors. "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."

Reference:

Tripathi O, Parada H, Sosnoff C, et al. Exposure to Secondhand Cannabis Smoke Among Children. JAMA Netw Open. 2025;8(1):e2455963. doi:10.1001/jamanetworkopen.2024.55963