Marijuana's Long-Term Impacts: Lighting Up Can Change Your Brain

More and more states are legalizing marijuana. And while many tout its medicinal properties, very little is known about its long-term impacts on a body. That's why scientists have taken a closer look, examining the long-term effects of marijuana on the human brain.

"We have seen a steady increase of marijuana use since 2007," said Francesca Filbey, one of the researchers, in a news release. "However, research on its long-term effects remains scarce despite the changes in legislation surrounding marijuana and the continuing conversation surrounding this relevant public health topic."

In order to better understand the effects of this substance, the researchers examined 48 adult marijuana users and 62 gender- and age-matched non-users. The scientists made sure to account for potential biases such as gender, age and ethnicity. In addition, they controlled for tobacco and alcohol use.

On average, the users consumed the drug about three times per day. Then the scientists conducted cognitive tests.

"What's unique about this work is that it combines three different MRI techniques to evaluate different brain characteristics," said Sina Aslan, one of the researchers. "The results suggest increases in connectivity, both structural and functional that may be compensating for gray matter losses. Eventually, however, the structural connectivity or 'wiring' of the brain starts degrading with prolonged marijuana use."

In fact, the scientists found that chronic marijuana users had lower IQ compared to age- and gender-matched controls. Yet the differences did not seem to be related to the brain abnormalities, since no direct correlation could be drawn between IQ deficits and OFC volume decrease.

Other tests, though, showed that earlier onset of regular marijuana use caused greater structural and functional connectivity. In fact, the greatest increase in connectivity appeared as an individual began using marijuana, and severity of use was directly correlated to greater connectivity.

"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," said Filbey.

The findings are published in the journal Proceedings of the National Academy of Sciences.