Using marijuana at an early age could have long-term consequences on your brain and it may even lower your IQ, according to a new study in the Proceedings of the National Academy of Sciences.

Researchers found that compared to nonusers, people who smoked marijuana starting as early as age 14 have less brain volume, or gray matter, in the orbitofrontal cortex. That’s the area in the front of your brain that helps you make decisions.

Dr. Francesca Filbey, the study’s principal investigator and associate professor at the School of Behavioral and Brain Sciences at the University of Texas at Dallas said “Adolescence is when the brain starts maturing and making itself more adult-like, so any exposure to toxic substances can set the course for how your brain ends up.”

Researchers also found increased brain connectivity in chronic users. Connectivity, when different parts of the brain connect to each other, is important for adaptive learning abilities. It also helps your mind make associations. This wiring of the brain starts to deteriorate with chronic marijuana use.

“Too much or too little of anything isn’t good. There needs to be an equal balance,” said Filbey.

Filbey said the people who regularly used marijuana had IQ’s that were five points lower, on average, than the nonusers in the study, although there is no definitive proof that marijuana alone was to blame for the lower IQ.

“While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age of onset and duration of use,” Filbey said.