CHICAGO, IL (CBS) – Think lighting up a joint every now and then is harmless?

New research out of Northwestern University and Massachusetts General Hospital/Harvard Medical School appears to dispute that belief.

The study, which was published in the April 16th issue of The Journal of Neuroscience, is reportedly the first to link casual marijuana use to brain abnormalities. It also showed that an increase in the number of joints smoked was linked to the degree of those abnormalities.

According to researchers, they studied the nucleus accumbens and amygdala, two key regions for emotion and motivation that are also associated with addiction, in the brains of both 20 pot smokers and 20 non-users between 18-25 years old. The scientists analyzed three measures — volume, shape and density of gray matter – to calculate how each region of the brain was affected by marijuana use.

What they found is that both brain regions were altered significantly in at least two measurements depending on how much pot the subject smoked. Scientists say their findings indicate that the subjects’ brains were adapting to low-level use of marijuana.

Scientists say that in animals, such adaptations show that the brain is becoming accustomed to the unnatural level of reward and stimulation from marijuana – connections that make other natural rewards less satisfying.

“Some of these people only used marijuana to get high once or twice a week,” co-senior study author Hans Breiter told ScienceNewsline. “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.”

And since a recent Northwestern study also showed chronic pot use was linked to brain abnormalities, Breiter says he’s “developed a severe worry about whether we should be allowing anybody under age 30 to use pot unless they have a terminal illness and need it for pain.”

For more information on the study, click here.

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