A new study finds teens who stop smoking marijuana for a month improve their ability to learn, HealthDay reports.

“Most of this improvement surprisingly happens rather quickly, within the first week of abstinence,” said lead author Randi Schuster of Massachusetts General Hospital’s Center for Addiction Medicine.

The study of 88 teens and young adults who used marijuana found those who stopped using the drug for a month showed improvement in the ability to learn and recall new information on computer tests. Those who did not stop using marijuana did not show such improvement.

Maturation of critical parts of the brain occurs during the teenage years, the researchers note in the Journal of Clinical Psychiatry. Regular marijuana use during those years may cause more harm than later use, they wrote.