Changes in Secondary Substance Use After the Onset of the COVID-19 Pandemic Among People Who Use Cannabis: Findings From a Web-Based Sample of Adults in the United States

The coronavirus disease 2019 (COVID-19) pandemic has had widespread impacts on mental health and substance use. Increases in cannabis use have been documented in the United States, but little is known about how other substance use has changed among people who use cannabis. We sought to examine changes in alcohol, tobacco, opioid, and stimulant use during COVID-19 and explore how these changes relate to patterns of cannabis use. Data were obtained from a web-based survey of adults in the United States who use cannabis (n = 1,471) administered in September 2020. Using data reported in retrospective (prepandemic) and time-of-survey assessment periods, we explored changes in the prevalence of regular (>= weekly) alcohol, tobacco, opioid, and stimulant use during COVID-19 among respondents who used medical and nonmedical cannabis. We used modified Poisson regression to examine cannabis-related correlates of increasing or decreasing secondary substance use during the pandemic. There was a slight but significant increase in >= weekly alcohol use in the medical use group only (41.4%-47.0%, p = .034). >= Weekly tobacco, opioid, and stimulant use did not change significantly. Pandemic-concurrent shifts in secondary substance use depended on interacting cannabis-related factors including medical cannabis use, prepandemic cannabis frequency, and pandemic-concurrent frequency changes. For example, >= weekly prepandemic cannabis use was significantly and positively associated with decreasing opioid use frequency among the medical cannabis use group only. Assessments of the pandemic's effects on substance use should consider relationships between cannabis and other substances, which may differ according to cannabis-specific behaviors, motives, and contexts of use. Public Health Significance This study suggests that, overall, >= weekly use of tobacco, opioids, and stimulants did not change substantially early after the onset of the coronavirus disease 2019 (COVID-19) pandemic in a sample of people who use cannabis. Modest group-level changes in alcohol use were detected among people who use medical cannabis. On an individual level, interaction between purpose, frequency, and COVID-concurrent changes in cannabis use influenced the likelihood of increasing or decreasing alcohol, tobacco, opioid, or stimulant use, highlighting cannabis-specific indicators of heightened vulnerability to the pandemic's effects on mental health and substance use.