Teens don't have to use marijuana that often for it to have a negative effect on their lives, according to a new study.

Even using marijuana once or twice a month is linked with worse school performance and more emotional turmoil among teenagers, researchers reported Tuesday in the journal Pediatrics.

And more frequent use brings even more emotional and academic problems, researchers found.

"Our study found that any amount of cannabis use at all may put kids at risk of falling behind in school, and the kids using most often may have the greatest risk," said the lead researcher, Dr. Ryan Sultan, an assistant professor of clinical psychiatry at Columbia University.

"A few 'harmless' joints can snowball into real academic consequences," he said in a news release. "Teens using it regularly often struggle to focus, miss school, and may lose interest in their future plans."

About 1 in 5 high school students use cannabis, and about 6% of high school seniors use it daily — a rate that has increased in the past decade, researchers said in background notes.

Particularly concerning is the fact that today's cannabis contains two to three times as much THC as it did in the past. THC is the compound that produces intoxication.

This potent weed could have a devastating impact on teenage brains, which are still developing crucial neural connections, researchers said.

"Using cannabis, even casually, during these critical growth periods interferes with those processes and can derail normal development," Dr. Tim Becker, a researcher and child and adolescent psychiatrist at Weill Cornell Medicine in White Plains, New York, said in a news release.

For the new study, researchers analyzed data from a survey of more than 160,000 eighth, 10th and 12th graders conducted from 2018 through 2022.

More than a quarter (26%) reported they had used weed at some time.

Among them, half said they aren't currently using it, 18% said they use it monthly, 14% weekly, and 18% nearly every day.

Those teens who said they use weed monthly were more than twice as likely to skip classes and have bad grades as nonusers.

Monthly users were also twice as lightly to get into fights; 72% more likely to seek danger; 40% more likely to prefer risk-seeking friends; 42% more likely to have difficulty experiencing joy and pleasure; and 32% to have a profound sense of emptiness and despair, results showed.

The risk of these negative behaviors and feelings rose as teens used cannabis more frequently, researchers found.

For example, near-daily users were nearly four times as likely to have bad grades or skip classes and activities, results showed.

And these associations were even stronger for younger weed users, researchers said.

Experts recommend having frank, nonjudgmental conversations about marijuana with your teen, early and often.

"Make sure they understand that 'natural' doesn't mean 'safe,'" Sultan said. "Parents also need to keep an eye out for warning signs like declining grades, mood changes, or loss of interest in hobbies — and consider that cannabis could be a factor."

More Information

The Centers for Disease Control and Prevention has more on marijuana and brain health.