Findings of a new study raise concern about the impact of recreational marijuana on teens. Researchers have found evidence showing that even a small amount of cannabis use in teenagers is associated with brain differences.

Brain Of Teens Who Used Recreational Marijuana

Hugh Garavan, from the University of Vermont School of Medicine, and colleagues looked at the brains of 46 kids from England, France, Ireland, and Germany who reported having used recreational marijuana once or twice by age 14.

MRI images revealed the kids who used weed have more gray matter volume in areas of the brain rich in cannabinoid receptors than kids who did not use the drugs.

The researchers also found the biggest difference in the volume of gray matter in the amygdala, which plays a role in fear and other emotion-related processes; and the hippocampus, which is involved in the formation of memory and spatial abilities.

"This study presents evidence suggesting structural brain and cognitive effects of just one or two instances of cannabis use in adolescence," the researchers wrote in their study, which was published in JNeurosci on Jan. 14.

Cannabis Use May Disrupt Pruning Process That Improves Brain Efficiency

The study did not indicate the meaning of the increased brain matter volume, but Garavan and colleagues said the enlargement of gray matter contradicts normal adolescent development.

Garavan explained that at age 14, cortical regions go through a process of thinning, suggesting that this is a "sculpting"' process that improves the efficiency of the brain and its connections.

"So, one possibility is that the cannabis use has disrupted this pruning process, resulting in larger volumes (i.e., a disruption of typical maturation) in the cannabis users," Garavan said. "Another possibility is that the cannabis use has led to a growth in neurons and in the connections between them."

Other Effects Of Cannabis Use To Teen Brain

The study is not the first to show the ill effects of cannabis use to the teen brain. In a 2017 study, researchers found weed can cause memory loss in adolescent users. Kids who smoke marijuana every day for years are also at increased risk of having abnormally shaped hippocampus.