Occasional marijuana use by young people appears to cause abnormalities in key areas of the brain, leading to new concerns that underage toking could lead to permanent neurological damage.

A study by researchers in Boston showed casual pot smoking by young adults caused abnormalities in two areas of the brain that moderate emotion, motivation, and decision-making. The scientists said the amount of damage increased with the amount of weed participants used each week.

This isn’t the first study to suggest that cannabis alters brain structures in young users. Previous research has shown the drug can change teenage brains in a fashion similar to schizophrenia.brain on marijuana

But this study is apparently the first to measure these kinds of changes in casual young smokers. It isn’t yet clear whether the damage seen by the researchers actually impairs brain functions, but expert Jodi Gilman said there’s reason to be concerned.

Gilman, the lead author of the study, is a psychology instructor at Harvard Medical School and a brain scientist at Massachusetts General Hospital.

“This is when you are making major decisions in your life, when you are choosing a major, starting a career, making long-lasting friendships and relationships,” Gilman said. If youthful marijuana use impairs brain functions, it could lead to poor choices at a critical time in life.

The study examined 40 young adults between the ages of 18 and 25 in the Boston area. Many are students at Boston University. Brain scans measured the volume, density, and shape of the two affected areas of the brain: the nucleus accumbens and the amygdala.

One half of the group, the control group, hadn’t smoked pot within the past year and hadn’t used it more than five times in their lives. The other half, the test group, smoked pot at least once a week – on average, six joints a week.

Brain scans showed the regular users had larger nucleus accumbens than the control group. The more the young person smoked, the larger the nucleus accumbens. There were also structural changes to the amygdala.

The nucleus accumbens regulates decision-making and motivation, while the amygdala moderates emotion and behavior.

seizures brain marijuanaGilman said these changes might involve the brain’s pleasure reward system. As drug use becomes regular, the brain can develop new neural pathways that encourage further use – sometimes leading to addiction. Gilman called this “a sort of drug learning process.”

But the study did not say whether the brain alterations are permanent.

Of course, marijuana isn’t the only substance to cause changes to the brain. Alcohol, cocaine, and other drugs all can lead to brain damage. That’s especially true since drug users tend to mix substances, said Dr. Hans Breiter, a co-author of the study.

“Most drug users use more than one drug,” said Breiter, professor of psychiatry and behavioral sciences at the Northwestern University School of Medicine. “Cocaine users use opiates, and most marijuana users also drink.”


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