How does smoking tobacco and cannabis affect depression risk?

People who use both cannabis and tobacco have significantly higher rates of depression and anxiety than those who use either substance alone or not at all, according to a new study by UC San Francisco researchers.

The study, published Sept. 13, 2023 in the online journal PLOS ONE, comes amid expanding legalization of cannabis products, resulting in more dual use with tobacco nationwide. Earlier studies relied on data collected before the legalization trend, prompting the need for a new analysis.

Understanding the association between the use of both drugs and mental health could lead to more effective prevention and treatment options, the paper’s authors said.

“We provide mental health treatment, but it’s not linked with support for cannabis and tobacco cessation,” said the paper’s lead author, Nhung Nguyen, PhD, assistant professor in the Division of General Internal Medicine at Zuckerberg San Francisco General Hospital and Trauma Center and a researcher with UCSF’s Center for Tobacco Control Research and Education. “We cannot provide tobacco cessation without addressing mental health or without considering cannabis use. These comorbidities are closely linked to tobacco use.”

A harmful combination

In conducting this study, the researchers were able to tap into an existing data source: the COVID-19 Citizen Science Study – a mobile app developed by UCSF researchers that contained a wealth of data, including mental health status and substance use, collected from participants around the country through online surveys.

They analyzed responses from 53,843 Americans from March 2020 to April 2022 who answered questions about tobacco and cannabis use over a 30-day period, and paired this with monthly assessments of the participants’ mental health status

Among people who used both substances, 26.5% reported anxiety and 28.3% reported depression. Percentages of anxiety and depression were only 10.6% and 11.2% in people who used neither substance. Those who only used tobacco had higher rates of anxiety and depression than those who did not.

The study did not delve into whether mental health conditions are exacerbated or triggered by tobacco or cannabis use or vice versa.

“Some believe that cannabis might mitigate against the ill effects of tobacco,” said the paper’s senior author, Gregory Marcus, MD, MAS, professor of medicine and associate chief of research for the Division of Cardiology, “But, these data suggest the combination is particularly harmful to mental health.”

Authors: Additional UCSF authors include Pamela Ling, MD, MPH, Noah Peyser, PhD, Jeffrey Olgin, MD, Mark Pletcher, MD, MPH, Alexis Beatty, MD, MAS, and Madelaine Modrow, MPH.

Funding and disclosures: The research is supported by the California Tobacco-Related Disease Research Program (grants T31FT1564 and T32KT5071) and the National Center for Advancing Translational Sciences, National Institutes of Health, through UCSF Clinical and Translational Science Institute (grant UL1 TR001872-06). The authors have no conflicts of interest to disclose.