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One Month of Cannabis Abstinence May Improve Users' Memory

Marijuana users (ages 16-25) learn better after four weeks of not smoking weed. 

 Stanimir G.Stoev/Shutterstock
Source: Stanimir G.Stoev/Shutterstock

Taking a four-week break from using marijuana may improve neurocognitive function in adolescents and young adults who regularly use cannabis, according to a new study from Harvard Medical School’s Massachusetts General Hospital (MGH). This study, “One Month of Cannabis Abstinence in Adolescents and Young Adults Is Associated With Improved Memory,” was published October 30 in the Journal of Clinical Psychology.

This new research from MGH is the first to prospectively track how cannabis abstinence changes cognitive function in the developing brain of young adults and adolescents who regularly used marijuana.

How Common Is Adolescent Cannabis Use?

A recent Health and Human Services (HHS) survey found that adolescent cannabis use is widespread and tends to increase during high school. In 2016, when asked, “Have you used marijuana in the past month?” five percent of students in 8th grade responded "yes." By 10th grade, this number was up to 14 percent and rose to 23 percent by the 12th grade.

For the new study on cannabis abstinence, the MGH researchers recruited 88 Boston-area residents and students ranging from 16 to 25 years of age who acknowledged regularly using cannabis at least once a week. Study participants were randomly assigned to four weeks of cannabis abstinence, which was verified by monitoring 11-nor-9-carboxy-∆9-tetrahydrocannabinol urine concentrations.

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Both randomized groups were paid for study visits. Notably, members of the group that was abstaining from cannabis were financially rewarded more generously for successfully achieving 30 days of continuous cannabis abstinence than the group that continued using pot regularly. In my opinion, monetizing participants' incentive to stay “drug-free” for a month could warrant a whole other study on addiction and how “token economies” can inspire people to refrain from substance abuse.

Throughout the month-long period of this study, attention and memory were assessed at baseline and on a weekly basis using the Cambridge Neuropsychological Test Automated Battery (CANTAB). Interestingly, the research findings suggest that significant improvements to verbal learning appear to occur in the first week following someone's last use of cannabis. The study also shows that the ability to ‘map down’ new information improved with four weeks of sustained nonuse of marijuana. No aspect of neurocognitive functioning or learning appeared to improve among participants in the control group that continued regular cannabis use.

“We can confidently say that these findings strongly suggest that abstaining from cannabis helps young people learn, while continuing cannabis use may interfere with the learning process,” Randi Melissa Schuster, director of neuropsychology at the Center for Addiction Medicine in the MGH Department of Psychiatry and lead author of this paper, said in an interview for Harvard's website. (MGH is a teaching hospital of Harvard Medical School.) “Our findings provide two pieces of convincing evidence. The first is that adolescents learn better when they are not using cannabis. The second—which is the good news part of the story—is that at least some of the deficits associated with cannabis use are not permanent and actually improve pretty quickly after cannabis use stops.”

The researchers are quick to point out that future studies are necessary to determine whether improvements in cognition associated with cannabis abstinence are also linked to better academic performance and other functional outcomes in day-to-day life. “There are still a lot of open questions to be studied, including whether attention might improve and memory continues to improve with longer periods of cannabis abstinence,” Schuster said.

The MGH team is planning a much larger follow-up trial. This study will include younger participants (ages 13 to 19) along with a cohort of study participants who have never used cannabis. Another upcoming clinical trial will investigate if cannabis abstinence results in cognitive improvements beyond a one-month period by having regular users abstain from marijuana use for six months. This research will also look specifically at a possible link between cannabis abstinence and better performance in school.


Randi Melissa Schuster, Jodi Gilman, David Schoenfeld, John Evenden, Maya Hareli, Christine Ulysse, Emily Nip, Ailish Hanly, Haiyue Zhang, and A. Eden Evins. "One Month of Cannabis Abstinence in Adolescents and Young Adults Is Associated With Improved Memory." Journal of Clinical Psychiatry (First published: October 30, 2018) DOI: 10.4088/JCP.17m11977