MRI shows how marijuana changes young brains

Researchers from Harvard Medical School and Northwestern University compared the brains of people (ages 18–25) who reported smoking marijuana at least once a week, but who were not dependent, to those with little or no history of drug using.

They found the heaviest users of marijuana had the greatest abnormalities of size, shape and density of the nucleus accumbens (involved in reward processing) and the amygdala (involved in emotion) compared to occasional or never users. However, even light users exhibited