Casual Marijuana Use Linked to Brain Changes in Young Adults
Light cannabis use by young adults might alter brain structure in two regions.
Published on April 22, 2014 by Christopher Bergland
Marijuana is the most commonly used illicit drug in the United States. Recent studies have shown that heavy marijuana use by young adults is associated with changes in brain structure linked to a loss of motivation, increased anxiety, and cognitive impairments.
A study from April 2014 has found that even light use of marijuana—smoking pot once a week—may cause structural changes in the size and shape of two brain regions. This is the first study to show casual use of marijuana may be related to major brain changes.
The study titled “Cannabis Use is Quantitatively Associated with Nucleus Accumbens and Amygdala Abnormalities in Young Adult Recreational Users” was published April 16 in The Journal of Neuroscience. The researchers found a direct correlation between the quantity of cannabis use and the degree of changes to the developing brain of people under 25-years-old.
4/15/2014 | For immediate release
BRAIN CHANGES ARE ASSOCIATED WITH CASUAL MARIJUANA USE IN YOUNG ADULTS
Preliminary study suggests effects of drug even in those who are not addicted
Washington, DC — The size and shape of two brain regions involved in emotion and motivation may differ in young adults who smoke marijuana at least once a week, according to a study published April 16 in The Journal of Neuroscience. The findings suggest that recreational marijuana use may lead to previously unidentified brain changes, and highlight the importance of research aimed at understanding the long-term effects of low to moderate marijuana use on the brain.
Marijuana is the most commonly used illicit drug in the United States, with an estimated 18.9 million people reporting recent use, according to the most current analysis of the National Survey on Drug Use and Mental Health. Marijuana use is often associated with motivation, attention, learning, and memory impairments. Previous studies exposing animals to tetrahydrocannabinol (THC) — the main psychoactive component of marijuana — show that repeated exposure to the drug causes structural changes in brain regions involved with these functions. However, less is known about how low to moderate marijuana use affects brain structure in people, particularly in teens and young adults.
In the current study, Jodi Gilman, PhD, Anne Blood, PhD, and Hans Breiter, MD, of Northwestern University and Massachusetts General Hospital/Harvard Medical School used magnetic resonance imaging (MRI) to compare the brains of 18- to 25-year olds who reported smoking marijuana at least once per week with those with little to no history of marijuana use. Although psychiatric evaluations ruled out the possibility that the marijuana users were dependent on the drug, imaging data revealed they had significant brain differences. The nucleus accumbens — a brain region known to be involved in reward processing — was larger and altered in its shape and structure in the marijuana users compared to non-users.
“This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy,” said Carl Lupica, PhD, who studies drug addiction at the National Institute on Drug Abuse, and was not involved with this study. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users.”
The team of scientists compared the size, shape, and density of the nucleus accumbens and the amygdala — a brain region that plays a central role in emotion — in 20 marijuana users and 20 non-users. 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 scientists 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.
“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” Breiter said.
This research was funded by the National Institute on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology Assessment Center, and the National Institute of Neurological Disorders and Stroke.
The Journal of Neuroscience is published by the Society for Neuroscience, an organization of nearly 40,000 basic scientists and clinicians who study the brain and nervous system.
The MRI brain images showed significant brain differences even in light marijuana users. In particular, the nucleus accumbens—which is a brain region linked to reward processing and motivation—was larger and altered in its shape and structure in the marijuana users compared to non-users. Of particular interest to the researchers was that the nucleus accumbens was abnormally large, and its alteration in size, shape and density was directly correlated to how many joints an individual had smoked.