Smoking cannabis reduces alcohol consumption in heavy drinkers, study finds

An experimental study of heavy drinkers found that smoking cannabis with 7.2% THC reduced their alcohol urge immediately after smoking. These participants consumed 27% less alcohol after smoking, while those smoking cannabis with 3.1% THC consumed 19% less alcohol. The research was published in the American Journal of Psychiatry.

Cannabis is a psychoactive plant that contains chemical compounds called cannabinoids. The most well-known cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is primarily responsible for the intoxicating effects, while CBD has non-intoxicating properties. CBD is studied for potential therapeutic uses.

Cannabis can be consumed by smoking, vaporizing, or ingesting extracts and edibles. The effects vary widely based on dose, potency, and individual sensitivity. Cannabis use leads to short-term changes in attention, memory, and coordination. In some individuals, it can trigger anxiety or paranoia. Long-term heavy use tends to lead to dependence, impaired cognitive functioning, or exacerbation of mental health conditions, particularly in vulnerable populations.

Some individuals use cannabis and alcohol together, but co-use can amplify impairment more than either drug alone. Alcohol is generally more often used as it is more socially accepted and is also legal in most jurisdictions. In contrast, cannabis is illegal in many countries around the world and more heavily stigmatized. However, the number of jurisdictions legalizing the use of cannabis is increasing.

Study author Jane Metrik and her colleagues wanted to explore how the consumption of cannabis affects cravings for alcohol and subsequent alcohol consumption. These authors note that results of previous studies on this are inconclusive. While some studies indicated that cannabis use might hinder alcohol dependence treatment and reduce abstinence, other studies reported no effects or even reduced consumption of alcohol after cannabis use.

The study randomized 157 individuals recruited from the community who endorsed the use of alcohol and cannabis; 138 participants completed at least two sessions and were included in the final analysis. Participants were required to be English speakers between 21 and 44 years of age, who had used cannabis during the past month two or more times weekly (and also two or more times weekly during the past 6 months), who had THC in their urine, who were familiar with smoking cannabis, and who were also prone to heavy episodic drinking of alcohol. Heavy episodic drinking was defined as having 5 or more alcoholic drinks per occasion for men and 4 or more drinks for women.

A standard alcoholic drink is defined as containing about 14 grams of pure ethanol. This is roughly equivalent to a small beer (350 ml), a glass of wine (150 ml), or a shot of spirits (45 ml).

All participants completed three experimental sessions in randomized orders. In one session they smoked cannabis with 3.1% THC, in another they smoked cannabis with 7.2% THC, and the third experimental session was a placebo session during which they smoked cannabis with almost no THC (0.03%). Experimental sessions were at least 5 days and no more than 3 weeks apart.

Before each experimental session, participants were told to abstain from cannabis and tobacco for 15 hours and from alcohol for 24 hours. They were also instructed to abstain from drinking caffeinated beverages for 2 hours before an experimental session.

Each experimental session started with a set of tests related to alcohol and cannabis levels, states related to the use of these substances, and several other assessments, including an assessment of alcohol craving. They also consumed lunch.

After this, participants smoked their assigned cannabis cigarettes. Next, they completed a test examining participants’ reactivity to alcohol cues (sight and smell of alcohol). In the end, they completed two alcohol choice tasks during which they were given an opportunity to either drink up to 8 mini-drinks of their choice or to receive $3 per drink not consumed.

Results showed that smoking cannabis had no effect on general cravings for alcohol (measured by the Alcohol Craving Questionnaire). Alcohol craving levels were similar in all three experimental conditions. However, after smoking 7.2% THC cannabis cigarettes, the specific urge to drink alcohol (measured by a single “urge” question) decreased significantly. Participants who smoked these cigarettes drank 27% less alcohol on average (compared to the placebo condition), while their alcohol consumption was 19% lower after smoking 3.1% THC cigarettes.

“Following overnight cannabis abstinence, smoking cannabis acutely decreased alcohol consumption compared to placebo,” study authors concluded.

The study contributes to the scientific understanding of the effects of cannabis on alcohol consumption. However, it should be noted that study participants were individuals who used cannabis frequently, with over 3 in 4 meeting criteria for current cannabis use disorder. They were also heavy alcohol drinkers. Because of this, they might have developed tolerance for the effects of these two substances. Results in individuals who use alcohol and cannabis less frequently might differ.

The paper, “Acute Effects of Cannabis on Alcohol Craving and Consumption: A Randomized Controlled Crossover Trial,” was authored by Jane Metrik, Elizabeth R. Aston, Rachel L. Gunn, Robert Swift, James MacKillop, and Christopher W. Kahler.