"The brain is much more vulnerable to insults like this sort while it is developing and they will need to do a bigger study where stringent controls are in place to include genetics, parental problems with marijuana, and psychopathology in the teen and the parent," said Leventhal. "These results do mean that we should make more effort in educating parents, schools and health officials on the dangers of early onset marijuana exposure."
And in a time when the legalization of marijuana is hotly debated, Seger said that the results are telling of a growing trend.
"With the lack of legalization, marijuanais getting stronger and stronger all the time," said Seger. "Many people who smoke pot don't want it to be legalized because it wouldn't be as strong once regulated and monitored."
Gruber agrees that the findings are significant as many states consider legalization of marijuana.
"We have to be clear about getting the message out that marijuana isn't really a benign substance," she said in a statement. "It has a direct effect on executive function. The earlier you begin using it, and the more you use of it, the more significant that effect."
Gruber also said it is unclear whether occasional marijuana use would have the same effect on cognitive function.
"It's impossible to tell whether our results would be the same in moderate smokers," said Gruber. "But there are even more of those people out there, so that will be the next place we go for our research."