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Brain Changes in Young Adult Recreational Cannabis Users

May 7, 2014

Brain Changes in Young Adult Recreational Cannabis Users

  1. Alain Joffe, MD, MPH, FAAP

Compared with nonusers, recreational cannabis users had greater gray-matter density and altered shape of the nucleus accumbens and amygdala.

  1. Alain Joffe, MD, MPH, FAAP

Most research on brain changes associated with marijuana use has been done in dependent, heavy users. In this magnetic resonance imaging study, the 20 young adult marijuana users (age range, 18–25; 11 females) did not meet criteria for dependence; on average they smoked almost 4 days and 11 joints per week. The 20 control subjects, who were matched for age, sex, handedness, race, and years of education (mean, 13 years), had smoked marijuana fewer than five times in their lifetime and not at all in the past year. Marijuana users consumed nonsignificantly more alcohol per week than controls (5.0 vs. 2.6 drinks) and scored higher on a measure of alcohol abuse (P=0.05).

Analyses were adjusted for age, sex, and alcohol and cigarette use. Whole-brain gray-matter density in the left nucleus accumbens and left amygdala was greater in marijuana users than in controls. Marijuana users and controls showed significant shape differences in the right amygdala and left nucleus accumbens. Gray-matter density in controls was correlated positively with volume and shape, but these relationships, especially in the left nucleus accumbens, were absent in marijuana users. Some of these differences were associated with the degree of marijuana exposure.

Comment

The brain areas affected in these young users — the amygdala and nucleus accumbens — are involved in reward processing and are implicated in the addiction process. In this cross-sectional study, whether brain changes preceded marijuana use cannot be determined. However, the results are consistent with similar findings in animal studies. Although the marijuana users did not meet criteria for dependence, they did report high levels of marijuana use. Determining whether similar changes occur in young adults who smoke less would be important.

  • Disclosures for Alain Joffe, MD, MPH, FAAP at time of publication Editorial boards Adolescent Medicine: State of the Art Reviews; JAMA Pediatrics

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