Study finds brain changes in young marijuana users

The Boston scientists found that the degree of brain changes appeared to be directly related to the amount participants smoked per week.

Young adults who occasionally smoke marijuana show abnormalities in two key areas of their brain related to emotion, motivation, and decision making, raising concerns that they could be damaging their developing minds at a critical time, according to a new study by Boston researchers.

Other studies have revealed brain changes among heavy marijuana users, but this research is believed to be the first to demonstrate such abnormalities in young, casual smokers.

The Boston scientists also found that the degree of brain changes appeared to be directly related to the amount participants smoked per week.

Researchers did not study whether those changes were linked to corresponding declines in brain function, but lead author Jodi Gilman, a psychology instructor at Harvard Medical School and a brain scientist at Massachusetts General Hospital, said such abnormalities in young brains are reason for concern.

“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.

Even casual marijuana use may alter neural pathways in the brain, according to a small study published in the Journal of Neuroscience. The researchers say they've turned up evidence of changes in the brain, which may be a possible sign of trouble ahead for recreational users.

The young adults who volunteered for the study were not dependent on pot, nor did they show any sign of marijuana-related problems in their daily lives.

"What we think we are seeing here is a very early indication of what becomes a problem later on with prolonged use," things like lack of focus and impaired judgment, said Dr. Hans Breiter, a study author.

The findings, published Wednesday in the Journal of Neuroscience, come amid an increased debate about the long-term effects of marijuana, as a growing number of states legalize the drug for medicinal and recreational use.

Forty Boston-area young adults aged 18 to 25, many from Boston University, were selected for the study. Researchers used scans to measure the volume, shape, and density of two regions of the brain - the nucleus accumbens and the amygdala.

Half of the group said they used marijuana at least once a week, and the other 20 had not used the drug in the past year, and reported using it less than five times in their life.

Among the group that did smoke, the median use was about six joints per week.

Scans revealed that the nucleus accumbens was larger in marijuana users, compared with nonusers, and its alteration was directly related to how much the person smoked. The nucleus accumbens is a hub in the brain that is involved with decision making and motivation. Structural changes were also seen in the amygdala, which is involved with emotional behavior.