People who use both tobacco and cannabis are more likely to report anxiety and depression than those who used tobacco only or those who used neither substance, according to a new study published this week in the open-access journal PLOS ONE by Nhung Nguyen of the University of California, San Francisco, U.S., and colleagues.

Tobacco and cannabis are among the most commonly used substances worldwide, and their co-use has been on the rise amid the expanding legalization of cannabis. In the new study, the researchers analyzed data on the substance use and mental health of 53,843 U.S. adults who participated in online surveys as part of the COVID-19 Citizens Health Study, which collected data from 2020 to 2022.

Overall, 4.9% of participants reported tobacco-only use, 6.9% reported cannabis-only use, and 1.6% reported co-use. Among people in the co-use group, 26.5% reported anxiety and 28.3% reported depression, while among people who used neither tobacco or cannabis, percentages of anxiety and depression were 10.6% and 11.2%.

The likelihood of having these mental health disorders were about 1.8 times greater for co-users than non-users, the study found. Co-use and use of cannabis only were also associated with higher likelihood of having anxiety compared to use of tobacco only.

This study cannot determine causation. However, the authors conclude that the co-use of tobacco and cannabis is associated with poor mental health and suggest that integrating mental health support with tobacco and cannabis cessation programs may help address this link.

The authors add, "Engaging in both tobacco and cannabis is linked to diminished mental well-being."