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Casual marijuana use linked to brain changes in young adults

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Although marijuana use is becoming more acceptable both socially and legally in many areas of our nation, including California, evidence continues to accumulate regarding its harmful effects. Many users of the substance are of the opinion that casual use is not harmful; however, a new study has reported casual marijuana use by young adults results in brain changes. The findings were published on April 15 in the Journal of Neuroscience journal by researchers at Northwestern University and Massachusetts General Hospital/Harvard Medical School.

The study authors note that marijuana is the most commonly used illegal drug in the US; according to the most current analysis by the National Survey on Drug Use and Mental Health, an estimated 18.9 million individuals report recent use. They note that use of the substance is often associated with motivation, attention, learning, and memory impairments. A number of studies have been conducted on animals exposed to tetrahydrocannabinol (THC), the main psychoactive component of marijuana. They report that repeated exposure to marijuana causes structural changes in brain regions involved with these functions. However, the authors of the current study note that less is known about how low to moderate marijuana use affects brain structure in humans, particularly in teens and young adults.

The study group comprise 20 marijuana users and 20 non-users who were aged 18 to 25. The marijuana users reported smoking the drug at least once per week. Each marijuana user was asked to estimate their drug consumption over a three-month period, including the number of days they smoked and the amount of the drug consumed each day. The researchers used magnetic resonance imaging (MRI) to compare the brains of the marijuana users to the non-users. 18- to 25-year olds who reported smoking marijuana at least once per week with similar individuals who did not use marijuana

Psychiatric evaluations ruled out the possibility that the marijuana users were dependent on the drug; however, MRI studies found that they had significant brain differences. The researchers found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and amygdala. The shape and density of both of these regions also differed between marijuana users and non-users. The nucleus accumbens, which is an area of the brain that is involved in reward processing, was larger and altered in its shape and structure in the marijuana users compared to the non-users.

Take home message:

Although the study group was small, the researchers found that even casual marijuana use can alter brain structure.

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