Children Exposed to Both Tobacco and Cannabis Smoke Have Higher Nicotine Levels
Young children whose mothers smoked both tobacco and cannabis had higher urinary cotinine levels than children of tobacco-only smokers, suggesting additive exposure effects.
Quick Facts
What This Study Found
Maternal co-smoking of tobacco and cannabis was associated with significantly higher children's cotinine levels (p=0.04) compared to tobacco smoking only, after adjusting for daily tobacco exposure, nicotine dependence, and other covariates.
Key Numbers
396 mother-child pairs. 36.9% of mothers also smoked cannabis in the past 7 days. Mean maternal age: 30.1 years. Mean child age: 30.2 months. Co-smoking significantly associated with higher children's cotinine (p=0.04) after adjusting for confounders.
How They Did This
Cross-sectional analysis of baseline data from the 'Babies Living Safe and Smokefree' RCT. 396 low-income mothers who smoked tobacco daily with children under 6. Multivariable regression testing whether maternal co-smoking predicted children's urinary cotinine levels.
Why This Research Matters
As cannabis use increases among parents, children may face compounded secondhand smoke exposure. This is the first study showing that dual tobacco-cannabis smoke exposure leads to higher nicotine metabolite levels in children than tobacco smoke alone.
The Bigger Picture
Public health messaging typically addresses tobacco and cannabis smoke separately. This study suggests their combined effects on children are additive, meaning co-use by caregivers creates a greater exposure burden than either substance alone.
What This Study Doesn't Tell Us
Cross-sectional design from a specific population (low-income tobacco-smoking mothers). Self-reported cannabis use may underestimate actual use. Cotinine reflects nicotine exposure specifically, not all smoke toxicants. Cannot assess long-term health outcomes for children.
Questions This Raises
- ?What are the long-term developmental effects of combined tobacco-cannabis smoke exposure in children?
- ?Would switching to non-combustion cannabis methods reduce children's exposure?
- ?How should pediatric screening address dual exposure?
Trust & Context
- Key Stat:
- Evidence Grade:
- Well-designed analysis with objective biomarker measurements and appropriate covariate adjustment, though limited to a specific population.
- Study Age:
- Published in 2026, addressing an emerging public health concern as cannabis normalization grows.
- Original Title:
- Association between children's secondhand co-exposure to tobacco and cannabis smoke and elevated urinary cotinine levels: a cross-sectional analysis.
- Published In:
- BMJ public health, 4(1), e003739 (2026)
- Authors:
- Collins, Bradley N(2), Lepore, Stephen J(2), Berardi, Vincent(3), Goodwin, Renee D, Wilson, Karen, Baishya, Mona
- Database ID:
- RTHC-08179
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis smoke add to children's tobacco smoke exposure?
Yes — this study found that children whose mothers smoked both tobacco and cannabis had significantly higher urinary cotinine (a nicotine metabolite) than children of tobacco-only smokers, even after accounting for how much tobacco the mothers smoked.
Should parents who use cannabis worry about secondhand exposure?
This study adds to evidence that combusted cannabis creates secondhand exposure for children. The additive effect with tobacco suggests parents who use both should be especially aware of exposure reduction strategies.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-08179APA
Collins, Bradley N; Lepore, Stephen J; Berardi, Vincent; Goodwin, Renee D; Wilson, Karen; Baishya, Mona. (2026). Association between children's secondhand co-exposure to tobacco and cannabis smoke and elevated urinary cotinine levels: a cross-sectional analysis.. BMJ public health, 4(1), e003739. https://doi.org/10.1136/bmjph-2025-003739
MLA
Collins, Bradley N, et al. "Association between children's secondhand co-exposure to tobacco and cannabis smoke and elevated urinary cotinine levels: a cross-sectional analysis.." BMJ public health, 2026. https://doi.org/10.1136/bmjph-2025-003739
RethinkTHC
RethinkTHC Research Database. "Association between children's secondhand co-exposure to tob..." RTHC-08179. Retrieved from https://rethinkthc.com/research/collins-2026-association-between-childrens-secondhand
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.