Young Women Who Used Cannabis and Tobacco at the Same Time Had Worse Cannabis Outcomes

What the researchers found

Using data from 3,427 young women, researchers distinguished between co-occurring use (using both substances in one's life) and simultaneous use (using cannabis and tobacco on the same occasion).

Regular cigarette smokers were 4.5-9.5 times more likely to also use cannabis and progress to cannabis abuse or dependence compared to non-smokers.

Among the 1,073 women who used both substances, those who used them simultaneously were 1.6 times more likely to meet criteria for DSM-IV cannabis abuse, even after controlling for early risk factors and prior cannabis use stages.

Twin analysis revealed that simultaneous use was not heritable (0% genetic influence) but was partly explained by shared environmental factors (31%), suggesting that peer groups and social contexts, rather than genetics, drive the behavior of combining these substances.

Why it matters

This study identified simultaneous cannabis-tobacco use as a marker for more severe cannabis outcomes. The finding that this behavior is environmentally (not genetically) driven suggests it may be modifiable through peer-based or contextual interventions.

The numbers in context

3,427 women total. Regular smokers: 4.5-9.5x more likely to use cannabis. 1,073 co-occurring users. Simultaneous users: 1.6x more likely to have cannabis abuse (OR 1.6). Heritability of simultaneous use: 0%. Shared environment: 31%.

How the study worked

Cross-sectional analysis of 3,427 young adult women from a twin registry. Distinguished co-occurring from simultaneous cannabis-tobacco use. Logistic regression examined associations with cannabis outcomes. Twin modeling estimated genetic and environmental contributions to simultaneous use.

What this study cannot tell us

Cross-sectional design cannot establish causation. Only women were studied. Self-reported simultaneous use may be imprecise. The cannabis-tobacco interaction mechanism was not investigated.

How to read the evidence

This is a well-designed twin study with a large sample, providing moderate evidence for the simultaneous use-cannabis outcome association and the environmental basis of this behavior.

When this study was published

Published in 2009. Research on cannabis-tobacco co-use has continued to identify it as a risk factor for worse outcomes.

The bigger picture

The distinction between co-occurring and simultaneous substance use is clinically important. Simultaneous use may involve different motivations, social contexts, or pharmacological interactions than simply using both substances at different times.

Questions still open

• Does tobacco pharmacologically enhance cannabis's addictive properties when used simultaneously? Would interventions targeting the social contexts of simultaneous use reduce cannabis problems?

Common questions

Read the original research

Simultaneous cannabis and tobacco use and cannabis-related outcomes in young women.

Drug and alcohol dependence, 101(1-2), 8-12

Citation

Agrawal, Arpana; Lynskey, Michael T; Madden, Pamela A F; Pergadia, Michele L; Bucholz, Kathleen K; Heath, Andrew C. (2009). Simultaneous cannabis and tobacco use and cannabis-related outcomes in young women.. Drug and alcohol dependence, 101(1-2), 8-12. https://doi.org/10.1016/j.drugalcdep.2008.10.019

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