Not only is cannabis the most commonly used illicit – in a number of states – drug among people who drink alcohol, cannabis is also by far the most commonly used illicit drug in the U.S. overall. New research findings tease out the nuanced relationship between alcohol and cannabis through a survey of regular cannabis users who also report drinking alcohol, as well as heavy drinkers in treatment who also use cannabis. These findings will be shared at the 44^th annual scientific meeting of the Research Society on Alcoholism (RSA), which due to the COVID-19 pandemic will be held virtually this year from the 19^th - 23^rd of June 2021.

“Given the increasing popularity and availability of cannabis products in the U.S. and worldwide, and the high frequency with which cannabis and alcohol are co-used, there are important public-health implications regarding the relationship between alcohol and cannabis use.” said Hollis Karoly, assistant professor in the department of psychology at Colorado State University. “Some data suggest that cannabis use is associated with increased drinking, while others indicate that cannabis may act as a substitute for alcohol and is thus associated with reduced drinking. There are also numerous individual factors that may impact this relationship, not all of which are currently well understood, such as the type or quantity of certain cannabinoids such as Δ⁹-tetrahydrocannabinol (THC) or cannabidiol (CBD) that people use.” THC is the main psychoactive compound in marijuana that what makes people feel "high," whereas CBD is non-psychoactive and its mechanism(s) of action throughout the brain and body are less well-understood.

Karoly will discuss her research findings at the virtual RSA meeting on 20 June 2021.

“Our survey data provided preliminary evidence suggesting that cannabis containing a higher THC:CBD ratio is associated with greater self-reported alcohol use compared to cannabis containing a lower THC:CBD ratio,” said Karoly. “We hypothesize that the mode of administration – for example, an edible, flower, or concentrated cannabis – may also play a role in this relationship, but no studies to our knowledge have explicitly tested this. Our survey study also found that that those who use cannabis to treat a medical condition may drink less often than those who use cannabis for non-medical purposes.”

The second study that will be discussed in the presentation concerns an eight-week intervention study for heavy-drinking individuals who wished to decrease their drinking. “We found that over the course of the study, and the three months following the study, individuals drank significantly fewer drinks and were significantly less likely to binge-drink on days when they used cannabis compared with days that cannabis was not used,” said Karoly.

Collectively speaking, and emphasizing that findings support associations rather than causal relationships, Karoly said that members of the public may use this information to inform their potential use of cannabis and alcohol. On the topic of alcohol and cannabis more broadly, she added, “numerous preclinical studies indicate that CBD may decrease alcohol consumption and reduce the behavioral markers of addiction in rodent models, but little is known about the impact of CBD on alcohol consumption in humans. The public should be aware that although CBD is often marketed as having numerous beneficial properties – including the capacity to reduce drinking or alleviate drinking-related harms – high-quality human data on this topic have not yet been published.”