The Dangers of Marijuana and Teenage Brains

A study published in the Journal of Neuroscience finds that even casual use of marijuana, once-a-week use, can lead to critical changes in the brains of 18- to 25-year-olds.

A collaboration between Northwestern University Medicine and Massachusetts General Hospital Harvard Medical School, the study is the first to prove the dangers of marijuana and teenage brains.  The more joints a person smoked, the more abnormal the shape, volume and density of the brain regions, the researchers found.

“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” corresponding and co-senior study author Hans Breiter, MD, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and a psychiatrist at Northwestern Memorial Hospital, said in a news release.

“Some of these people only used marijuana to get high once or twice a week,” Breiter said. “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.”

Public health officials have known for some time that marijuana can produce the damaging, long-term brain changes required to establish physical dependence and addiction. However, no one really knows the precise point at which marijuana-related brain damage starts to occur. The new research concludes that very low levels marijuana intake do indeed trigger unusual changes in two important brain areas.

Marijuana and other common substances of abuse are problematic because their use upsets the normal balance of chemicals in the brain’s pleasure center and triggers an unusually pleasurable state called euphoria. If a substance user tries to repeatedly access this euphoric state, the temporary chemical alterations in the pleasure center may gradually become long-term shifts in the brain’s everyday environment and lead to the beginning of substance dependence. In turn, many people affected by substance dependence will go on to develop urgent substance cravings, a loss of control over substance intake and a range of other problems that mark the onset of full-fledged substance addiction.

While marijuana has a largely benign reputation in broad segments of the U.S. population, current scientific evidence indicates that about 9 percent of all people who use the drug to any extent will eventually develop a diagnosable case of cannabis/marijuana addiction. Teenagers who use the drug even occasionally develop diagnosable symptoms of addiction at nearly twice this rate. However, the starkest risks for cannabis/marijuana addiction occur among people of any age who use the drug every day or nearly every day; addiction rates for these individuals are at least 25 percent and may rise as high as 50 percent.

Brain Damage Linked to Pot

In addition to the dysfunctional changes that directly set the stage for dependence and addiction, repeated marijuana use can lead to damaging changes in brain areas that play critical roles in forming and maintaining the higher-level mental functions that make human beings distinct as a species. One of these brain areas, called the nucleus accumbens, helps people do such things as learn from their mistakes, control impulsive behavior and process certain strong emotions. Another affected area, called the amygdala, also helps people process strong emotions, in addition to playing a vital part in memory processing and the ability to make decisions. Problems in both of these brain areas are linked to the establishment and reinforcement of a highly substance-oriented outlook in people affected by addiction.

Potential Consequences of Casual Use

In the study published in The Journal of Neuroscience, researchers used a scanning procedure called MRI (magnetic resonance imaging) to compare the brains of 20 young adults who used marijuana a minimum of once weekly to the brains of 20 young adults who never or rarely used marijuana. The participants in both groups were between the ages of 18 and 25. The researchers characterized the participants in the marijuana-using group as “light-to-moderate casual users,” they employed standard psychiatric testing to make sure that none of these individuals met the criteria used to diagnose cannabis/marijuana addiction.

After comparing the MRI results of the two groups, the researchers found that both the nucleus accumbens and the amygdala in the brains of the casual marijuana users were shaped differently, had a different size and had changes in normal density when compared to the same brain areas in the participants who seldom or never used marijuana. When they tracked the level of overall consumption and the number of individual days on which marijuana was consumed, they also found that those individuals with a greater level of involvement in drug use were more affected by these changes than those individuals closer to the baseline level of casual intake.

The authors of the study published in The Journal of Neuroscience believe that their findings indicate that even casual marijuana users may start to experience the damaging brain changes that can ultimately reinforce cannabis/marijuana addiction. They specifically point toward the relative likelihood of these changes in heavier casual users who still don’t qualify for an official addiction diagnosis, and note that the presence of brain alterations in these individuals runs counter to the popular belief that casual marijuana intake is essentially a risk-free activity.

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