Countless college students have conducted the experiment: What happens when you mix alcohol and cannabis?
But few have done so in a lab, under the watchful eye of scientists, carefully calibrating their breathing as they take hits of research-grade marijuana.
In a new study, investigators corralled around 150 adults into a makeshift bar on campus at Brown University in order to test how much people wanted to drink after they smoked cannabis. It is one of the first rigorous trials to examine how marijuana affects drinking.
“This is basically a very carefully, precisely designed study of cross-fading,” said Dr. James MacKillop, the director of the Michael G. DeGroote Center for Medicinal Cannabis Research at McMaster University and an author on the study. (Cross-fading means getting simultaneously drunk and high.)
The researchers found that people drank considerably less after they smoked cannabis.
The new paper, published Wednesday, arrives at a time when going “California sober” — using marijuana and other drugs, but not alcohol — has become trendy. Researchers attribute its popularity to the growing legalization and availability of cannabis in an array of forms, including prepackaged edibles and beverages, as well as a rising awareness about the health harms of alcohol.
“We too often study drugs in isolation,” said Ryan Vandrey, a professor of psychiatry and behavioral sciences at Johns Hopkins Medicine, who studies cannabis and was not involved with the new research. But in reality, he said, people commonly combine alcohol and cannabis.
“We don’t have a good understanding of that,” he said. “And I think we need it.”
The researchers recruited 157 people who regularly use both cannabis and alcohol. The experiment took place over three rounds, separated days apart. During one session, participants smoked joints with a higher concentration of THC, a psychoactive compound in cannabis. In another session, they smoked cannabis with less THC, and in a third, they smoked a placebo joint.
Cannabis intake was controlled; the participants followed a standardized “paced puffing procedure,” listening to an audio tape instructing them when to inhale and exhale.
After they smoked, they went to a lab that was designed to look like a bar, decorated with string lights and signs for Guinness and Jack Daniel’s. The bar was stocked with the participants’ drinks of choice. The researchers watched through a two-way mirror as the participants weighed whether they wanted a drink.
On the day they smoked the higher-THC cannabis, participants drank around a third less than they did on the day they smoked the placebo joint. After they smoked the lower-THC cannabis, they consumed around twenty percent less alcohol than when they used the placebo.
Despite the study’s findings, it’s far too early to say for sure that cannabis can curb drinking, said Jane Metrik, a professor of behavioral and social sciences at the Brown University School of Public Health and the lead author on the paper.
And because the study was so controlled, the results might not neatly translate into everyday life. Popular marijuana products typically contain far more THC than even the higher dose used in the trial, said Johannes Thrul, an associate professor at the Johns Hopkins Bloomberg School of Public Health, who was not involved with the trial. (As with many studies, the scientists sourced cannabis from a national supply specifically used for research.)
As more potent cannabis hits the market, researchers are eager for more data on how the drug might interact with alcohol. There are still many unknowns about the combined health effects of both alcohol and marijuana: how the substances work in concert in the body; how different cannabis compounds mix with alcohol; and if smoking, eating or drinking marijuana changes how it intersects with alcohol.
“At the end of the day, it will have to be these really tightly controlled laboratory studies and then the real-world evidence coming together to paint the picture,” Dr. Thrul said. “Because none of these studies can answer these questions by themselves.”
Dani Blum is a health reporter for The Times.
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