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New study links casual marijuana use with changes in brain

UNDATED (KOKH) -- A new study released Tuesday suggests that casual marijuana use may damage your brain.

The study, published in the Journal of Neuroscience, links casual marijuana use to changes in the brain. Researchers say the degrees of abnormalities in the brain is based on the number of joints smoked in a week.

Researchers used different types of neuroimaging to examine the brains of 40 college students. They ranged in age between 18 and 25 and were all enrolled in Boston area colleges. Half of the students smoked pot at least once a week while the other half didn't smoke at all.

The smokers were asked to track their cannabis use for 90 days.

All the participants were given high-resolution MRIs, and researchers compared their results.

Researchers studied the nucleus accumbens and amygdala, the parts of the brain involved in emotional processing and motivation and reward. They analyzed the volume, shape and density of grey matter where most cells in brain tissue are located.

"I think the findings that there are observable differences in brain structure with marijuana even in these young adult recreational users indicate that there are significant effects of marijuana on the brain," says Dr. Jodi Gilman, lead author and a researcher in the Massachusetts General Center for Addiction Medicine. "Those differences were exposure-dependent, meaning those who used more marijuana had greater abnormalities."

Seven out of 20 of the participants only used pot once or twice a week. The median use was six joints a week, but there were four people who said they smoked more than 20 joints a week. None of the users reported any problems due to their use, in school, with the law or otherwise.

"There's a general idea out there that casual use of marijuana does not lead to bad effects, so we started out to investigate that very directly," Dr. Hans Breiter says. "This research with the other studies we have done have led me to be extremely concerned about the effects of marijuana in adolescents and young adults and to consider that we may need to be very careful about legalization policies and possibly consider how to prevent anyone under age 25 to 30 from using marijuana at all."

Researchers have always been concerned with how marijuana affects the brains of people under 25-years-old. Some research suggests that smokers who start young are slower to complete tasks, have lower IQs later in life and have an increased risk of having a stroke.

"This data certainly confirms what others have reported with regard to changes in brain structure," says Dr. Staci Gruber, the director of Cognitive and Clinical Neuroimaging Core at McLean Hospital and Harvard psychiatry professor. "When we consider the findings of the Gilman ... study with our own and other investigations of marijuana use, it's clear that further investigation is warranted, specifically for individuals in emerging adulthood, as exposure during a period of developmental vulnerability may result in neurophysiologic changes which may have long-term implications."

Gruber also says that we need to do more research on all pot users and their rate of use. She also says that using marijuana before the age of 16 is associated with difficulty in doing tasks requiring judgment, planning and inhibitory function as opposed to those who start later.

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