High school students who use tobacco and cannabis products miss more school and have lower grades than classmates who use them individually or not at all.

That’s the conclusion of a study by researchers at UC Davis Health.

“Substance use is a main predictor of educational outcomes, including absenteeism,” said first study author Melanie Dove, an assistant adjunct professor of public health sciences at UC Davis. “These results highlight the need for comprehensive efforts to prevent and reduce substance use from both cannabis and tobacco products among youth.”

For the study, her team analyzed 2021-22 data from the California Healthy Kids Survey. It included more than 287,600 ninth- and 11th-graders.

Of that group:

  • 3.7% used tobacco and cannabis

  • 3.7% used cannabis only

  • 1.7% used tobacco only

Those who used both products missed an average three days of school in the preceding month — twice as many as teens who didn’t use both. 

Their grades suffered, too. 

On an 8-point scale with an 8 representing A’s and a 1 representing F’s, nonusers averaged about 6.2, mostly Bs. In comparison, double users averaged about 5.1 (mostly Bs and Cs), the survey showed.

Classmates who used one substance also had poorer grades than abstainers. Tobacco users averaged 5.6; cannabis users averaged about 5.5 — or mostly B’s for both groups.

The findings were recently published online in The Journal of Pediatrics.

A study co-author pointed to a U.S. Surgeon General’s report that explained how habits formed when the brain is still developing can result in teens getting addicted more easily.

“We know that using tobacco and cannabis puts young people at risk for longer-term addiction, behavioral issues and respiratory health problems,” said Dr. Elisa Tong, director of the Tobacco Cessation Policy Research Center at UC Davis.

“For young people who are not current users but are exposed to use by others, the aerosol from these products is not harmless, and contains potentially harmful chemicals, heavy metals and fine particulates,” she added in a UC Davis news release.

Researchers noted that the study had some limitations.

The results differ sharply from those of the 2022 California Youth Tobacco Survey. In that survey, 6.6% of students said they use tobacco — a much higher rate than the current study but well below the 12.6% national average.

“While certain school factors — like peer pressure — can contribute to teen tobacco and cannabis use, schools also play a critical role in prevention, especially in partnership with families,” said senior study author Kevin Gee, a professor of education at UC Davis.

More information

There’s more about the impact of marijuana use on teen health at the U.S. Centers for Disease Control and Prevention.

SOURCE: UCDavis Health, news release, March 14, 2024