Children Exposed to Both Tobacco and Cannabis Smoke Have Higher Nicotine Levels | Research

The takeaway

Young children whose mothers smoked both tobacco and cannabis had higher urinary cotinine levels than children of tobacco-only smokers, suggesting additive exposure effects.

Parents who smoke, pediatric healthcare providers, public health professionals, and anyone concerned about children's environmental exposure.

What the researchers 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.

Why it 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 numbers in context

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 the study worked

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.

What this study cannot 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.

How to read the evidence

Well-designed analysis with objective biomarker measurements and appropriate covariate adjustment, though limited to a specific population.

When this study was published

Published in 2026, addressing an emerging public health concern as cannabis normalization grows.

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.

Questions still open

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?

Common 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 the original research

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

View on PubMed ↗Publisher’s paper ↗

Citation

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