This further solidifies the suggestion that early marijuana use can have long-term consequences on the brain.
A new paper from scientists at the Center for BrainHealth at the University of Texas at Dallas suggests that the age at which a teen begins smoking marijuana may affect the typical course of brain development.
Study findings reveal that participants who began smoking marijuana at the age of 16 or younger showed arrested brain development in the prefrontal cortex, which is the part of the brain that’s responsible for judgment, reasoning, and complex thinking. On the contrary, those who started smoking weed after the age of 16 showed the opposite effect — they demonstrated signs of accelerated brain aging.
"Science has shown us that changes in the brain occurring during adolescence are complex. Our findings suggest that the timing of cannabis use can result in very disparate patterns of effects," principal investigator Francesca Filbey, Bert Moore Chair of Behavioral and Brain Sciences at the Center for BrainHealth, said in a press release.
"Not only did age of use impact the brain changes but the amount of cannabis used also influenced the extent of altered brain maturation," she said.
The team analyzed MRI brain scans of 42 heavy marijuana users — 20 were categorized as “early onset” users, with a mean starting age of 13.18 years. The other 22 were labeled as “late onset” users, with a mean age of 16.9 years.
They were labeled as heavy marijuana users based on their self-reported data. All of the participants, ages 21 to 50, began smoking pot during their teenage years and continued the habit throughout adulthood, smoking at least once a week.
Now, first and foremost, what does typical adolescent brain development look like?
According to Filbey, the brain “prunes” neurons during adolescent brain development, which results in reduced cortical thickness and greater gray and white matter contrast. This pruning also leads to more gyrification in the brain, which means more wrinkles and folds on the brain’s surface.
After analyzing the MRI results, the researchers found that the more marijuana smoked by early onset users, the greater their cortical thickness, the less grey and white matter contrast, and the less intricate the gyrification was in comparison to late onset users. The extent of brain alteration was directly proportionate to the number of weekly marijuana uses in years and grams consumed, the researchers say.
In contrast, those who began smoking marijuana after the age of 16 showed brain changes that would typically occur later in life: thinner cortical thickness and stronger grey and white matter contrast.
"In the early onset group, we found that how many times an individual uses and the amount of marijuana used strongly relates to the degree to which brain development does not follow the normal pruning pattern,” said Filbey. “The effects observed were above and beyond effects related to alcohol use and age.”
Filbey says that these findings align with the common argument that cannabis use during adolescence can have long-term consequences. Marijuana continues to gain acceptance for both medicinal and recreational uses, but it’s important — particularly for teenagers — to understand the risks before indulging.