It might take no more than a single joint to impact brain development in teens, according to science.
Researchers from the University of Vermont recently sought to find out what the effects of "extremely low levels of cannabis" were on teen brains. And as the study's lead author Dr. Hugh Garavan says, the team was "surprised by the large effects we found."
Garavan and his researchers looked at a set of 47 brain scans taken from teens who had consumed cannabis no more than twice by the age of 14. That might not seem like much exposure at all, but the team found that even consuming a little cannabis at a young age can change the adolescent brain.
"We see very many brain regions in which grey matter volume is greater in the cannabis users and it was surprising to think that these could be the result of just one or two uses," Garavan told Inverse.
It may sound like a good thing that these young people had bigger brains than their peers who had not consumed cannabis, Garavan says that's not the case. During this period of a person's development, brains are actually expected to get smaller.
"At the age at which we studied these kids, cortical regions are going through a process of thinning—the idea is that this is a 'sculpting' process that makes the brain and its connections more efficient," said Garavan. "If cannabis is affecting this process then it is reasonable to suspect that it could lead to cognitive differences."
But Garavan stress that he can't yet prove cannabis is actually behind the changes in brain volume, nor can he state what, if any, cognitive differences will occur.
"Given that we don't understand the exact brain mechanisms underlying the observed effect and we don't know what explains the differences between users, we should be cautious before drawing firm conclusions," he said.
Still, he believes his study should be used as warning and young teens should be encouraged to avoid the substance until we have a better understanding of the potential risks.