Marijuana may boost risky effects of drinking alcohol

A new study from Penn State found that compared to people who only drank alcohol, those who used alcohol and marijuana simultaneously were more likely to drink heavier and more often. They were also more likely to experience alcohol-related problems -- like impulsive actions they later regretted.

"The results suggest that individuals who simultaneously use alcohol and marijuana are at a disproportionately higher risk for heavy, frequent, and problematic substance use," said Ashley Linden-Carmichael, assistant research professor at the Edna Bennett Pierce Prevention Research Center at Penn State.

The researchers said the findings -- recently published in the journal Substance Use and Misuse -- also suggest that prevention and intervention programs should take into account not just alcohol, but also if people are using additional substances, as well.

"Right now, a lot of campus programs focus on whether students are drinking, and while sometimes they are asked about other substances, it's not necessarily whether they're using these substances simultaneously," Linden-Carmichael said. "I think we do need to be asking about whether they're drinking in combination with other drugs and educating students about how that exacerbates their risk."

According to the researchers, marijuana use is at an all-time high among young adults in the U.S., possibly leading to people using marijuana and alcohol simultaneously.

"The problem with simultaneous use is that it can affect people cognitively and perceptually, and also have an impact on motor impairment," Linden-Carmichael said. "There is a burgeoning area of research that is examining why people are using marijuana and alcohol together and what those effects are."

In the study, Linden-Carmichael said she and the other researchers were interested in learning more about how people use marijuana and alcohol together. They also wanted to explore whether personality traits -- like the tendency to pursue new and exciting experiences, or "sensation seeking" -- were associated with higher odds of using alcohol and marijuana at the same time.

The researchers recruited 1,017 participants from 49 states in the U.S. between the ages of 18 and 25 for the study. The participants provided information about how often they used alcohol, marijuana and the two substances simultaneously. They also filled out questionnaires that measured their experiences with alcohol-related problems, whether they had a sensation-seeking personality, and how they perceived the drinking habits of their friends.

Linden-Carmichael said that across the board, individuals who used alcohol and marijuana simultaneously were at a greater risk than individuals using alcohol alone.

"Even after controlling for the number of drinks a person typically consumed, people who used alcohol and marijuana at the same time were at a greater risk for problems like blacking out, getting in an argument, or other concerns," Linden-Carmichael said. "Additionally, 70 percent of those who engaged in simultaneous use reported using at least weekly."

The researchers found that among people who used alcohol and marijuana simultaneously, those who used more frequently were more likely to drink more alcohol, more often, and for longer periods of time. They were also associated with using more marijuana more often.

Additionally, they found that people who used alcohol and marijuana together were more likely to have higher levels of sensation-seeking characteristics and think their friends were drinking larger amounts of alcohol.