BOSTON (CBS) — Scientists at Harvard and Massachusetts General Hospital have found marijuana is bad for the young brain.

Researchers performed brain scans on 40 young adults between 18-25 years old, and found the more pot smoked, the more abnormalities they found in two key areas of the brain which affect emotion, motivation and decision-making.

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Half of the group said they used marijuana at least once a week, and the other 20 had not used the drug in the past year, and reported using it less than five times in their life.

Among the group that did smoke, the median use was about six joints per week.

The study’s lead author, Jodi Gilman, a psychology instructor at Harvard Medical School and a brain scientist at Mass. General Hospital says the results should deter young people from smoking.

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“The study shows we should be cautious of it and discourage it in adolescents and young adults where the developing brain may be more susceptible to cannabis-induced changes,” Gilman told WBZ NewsRadio 1030.

Noting larger studies are needed, Gilman said the study did not conclude whether the effects are minimized once a person stops smoking marijuana.

“The study shows there are effects on the brain from marijuana,” Gilman said. “The next thing is looking at how structural abnormalities effect clinical outcomes; who will become addicted to marijuana?”

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