While some medical theorists claim cannabis can help you. others might say instead that it hurts you. New research published this month may support the latter theory. Marijuana, it seems, is not a performance-enhancing drug. That is, at least, not among young people, and not when the activity is learning.

A study published in the Journal of Clinical Psychiatry finds that when adolescents stop using marijuana – even for just one week – their verbal learning and memory improve. The study contributes to growing evidence that marijuana use in adolescents is associated with reduced neurocognitive functioning.

More than 14 percent of students in middle school and high school reported using marijuana within the past month, finds a National Institutes of Health survey conducted in 2017. And marijuana use has increased among high-schoolers over the past 10 years, according to the U.S. Department of Health & Human Services.

At the same time, the percentage of teens who believe that regular marijuana use poses a great risk to their health has dropped sharply since the mid-2000s. And legalization of marijuana may play a part in shaping how young people think about the drug. One study noted that after 2012, when marijuana was legalized in Washington state, the number of eighth-graders there that believed marijuana posed risks to their health dropped by 14 percent.

Researchers are particularly concerned with marijuana use among the young because THC, the active ingredient in marijuana, most sharply affects the parts of the brain that develop during adolescence.

“The adolescent brain is undergoing significant neurodevelopment well into the 20s, and the regions that are last to develop are those regions that are most populated by cannabis receptors and are also very critical to cognitive functioning,” says Randi Schuster. Schuster is the director of neuropsychology at Massachusetts General Hospital’s Center for Addiction Medicine and the study’s lead author.

Schuster and the team of researchers set out to determine if cognitive functions that are potentially harmed by marijuana use in adolescents – particularly attention and memory – improve when they abstain from marijuana.

They recruited 88 pot-using teens and young adults, ages 16 to 25, and got some of them to agree to stop consuming marijuana for the month.

The researchers randomly assigned the volunteers into an abstaining group and a nonabstaining group. They delivered the bad news to those chosen to be abstainers at the end of their first visit, and Schuster says, they took it surprisingly well.

Also at each visit, the participants completed a variety of tasks testing their attention and memory through the Cambridge Neuropsychological Test Automated Battery, a validated cognitive assessment tool.

Interestingly, most of the memory improvement for the abstinent group happened during the first week of the study, which leaves the researchers feeling hopeful.

The researchers found that after four weeks, there was no noticeable difference in attention scores between the marijuana users and the nonusers. But, the memory scores of the nonusers improved, whereas the users’ memories mostly stayed the same.

While this study didn’t prove that abstaining from cannabis improves adolescents’ attention, other studies have found that marijuana users fare worse in attention tests than nonusers. Schuster hypothesizes it might take more than four weeks of abstinence for attention levels to improve.

“We were pleasantly surprised to see that at least some of the deficits that we think may be caused by cannabis appear to be reversible, and at least some of them are quickly reversible, which is good news,” Schuster says.