Lower grades for students who use both tobacco and cannabis, California survey reveals

By Dr. Liji Thomas, MDReviewed by Danielle Ellis, B.Sc.Mar 18 2024

Several reports have raised the issue of increasing absenteeism and lower grades in American public schools after they reopened following the coronavirus disease 2019 (COVID-19) pandemic. These predict higher rates of mental illness and dropout from high school. Substance use is also linked to poor outcomes, including vaping, tobacco, and cannabis, perhaps because of their effects on the developing brain.

A recent study published in The Journal of Pediatrics examines the odds of these outcomes when tobacco and cannabis are co-used after compensating for other risks. With the rise in legalized cannabis, there has been an increase in the national (but not California) proportion of young people who vape, from 11% to 21% over the period 2017 to 2022. Again, the proportion of cannabis users went up from 5% to 15%.

The current study sought to dissociate this risk in a sample of high school students in California surveyed in 2020-21, immediately after post-COVID school reopening.

About the study

The study utilized the California Healthy Kids Survey (CHKS), performed by the WestEd, the California Department of Education, and the Department of Health Care Services, on students in grades 9 and 11 in California. Only public school students were included, numbering about 353,000, who responded to survey questions about tobacco and cannabis use during the 30 days just before the survey and were attending school in person.

The sample was equally split between males and females, grades 9 and 11, and those with highly educated parents vs others. Almost half were Hispanic, a quarter non-Hispanic White, and 15% Asian. Over one in three said they had felt depressed sometime in the past year, while 6% reported feeling endangered at school.

Almost a tenth used alcohol, while 2% used tobacco alone. About 4% used cannabis, and the same proportion used both substances. Almost double these numbers were reported as having used these substances at any time.

Co-use of both substances was linked to 35% absenteeism vs 29% in cannabis-only users, 26% among tobacco-only users, and 17% among those who used neither. Risk factors for absenteeism and/or poor grades that needed to be adjusted for included bullying, poor health, and change of residence if the student is a caregiver for others or comes from a family with food insecurity. Unsafe school conditions or poor educational climates at school also play a role in this phenomenon.

After adjustment, co-users had a 40% higher risk of absenteeism, the highest among all categories. Compared to tobacco-only users, co-use and cannabis-only users both were ~20% and 15% more likely to report absenteeism, respectively. Similar findings were obtained among ever-users, too.

The mean grade was 6.16, that is, mostly Bs. Co-use was associated with a mean grade of 5.08 vs 5.61 for tobacco-only users, 5.54 for cannabis-only users, and 6.24 among non-users. If using tobacco only was the reference group, co-users, and cannabis-only users had a decrease of 0.39 points, but it fell by a mean of 0.87 points when co-users were matched to non-users. Cannabis-only and tobacco-only users had no difference in their mean grades.

Dangers of absenteeism

School funding suffers when students are absent. Thus, co-use has roughly cost the school $300 per absent student on average.

With over 8,000 students reporting substance use, absences may potentially have cost the school almost $2.5 million in annual funding, provided all of these absences were due to substance use, though this is an unlikely event.

What are the implications?

The drop in grades by almost one category, from Bs to Bs and Cs, associated with co-users compared to non-users, is an important adverse effect. This was accompanied by 40% higher odds of absenteeism (being absent three or more days within the past month) in the co-user group vs non-users and 20% higher odds than among tobacco-only users.

This novel study supports the hypothesis that substance abuse, especially the dual use of tobacco and alcohol, worsens educational outcomes. Several mechanisms have been speculated about. For instance, these substances could affect cognitive processing and disrupt learning and memory pathways.

Cannabis heightens nicotine addiction when used during adolescence, making quitting very difficult. Also, the use of either or both of these substances can cause illness, physical or mental, resulting in skipping school. Co-use has been linked to changes in the sleep pattern.

Finally, vaping at school may distract students, reducing their ability to learn. Another possibility is that vaping or co-use may result in suspension from school. The occurrence of such events is mirrored in the list of reasons for absenteeism, such as illness, anger, sadness, stress, or inadequate sleep.

Future studies should assess potential interventions to improve educational outcomes with the help of full-spectrum efforts to reduce or eliminate substance use among students.