Casual marijuana smokers might want to reconsider their smoking habits, according to a new study published in the Journal of Neuroscience.

A collaboration between Northwestern Medicine and Massachusetts General Hospital/Harvard Medical School, the study researched recreational marijuana use and ultimately discovered significant abnormalities in two vital brain regions important in emotional processing and motivation.

The degree of abnormalities found depended on the number of joints the participants (all 18 to 25 years old) smoked weekly. Even those who smoked once a week showed brain abnormalities, while larger changes were observed in those who smoked more, The Washington Post reported.

Researchers arrived at this conclusion by analyzing volume, shape and density grey matter, the area where most cells in brain tissue are located. 

"This study raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences," said co-author Hans Breiter, M.D.

"People think a little recreational use shouldn't cause a problem, if someone is doing OK with work or school. Our data directly says this is not the case."

According to the National Survey on Drug Use, almost 19 million people in the U.S. used marijuana in 2012. As for young adults, 60 percent of American high school seniors do not see regular marijuana use as harmful to their health.

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