However, scientists do not yet know whether genes are solely to blame.

“There are two possible types of predisposition,” said Breiter. “Either the amygdala was going to develop normally, but the drug caused it not to, or the amygdala was never going to develop normally in the first place.”

Regardless, Breiter said that these findings will cause major public policy changes in the future.

“If cocaine causes the amygdala to change in shape, it means that we have a mandate to get it off the street,” said Breiter. “If this is purely genetic, then we should develop better medical diagnosis and prevention skills—we can determine who is at risk.”

The study is part of the greater Phenotype Genotype Project in Addiction and Depression, the largest neuro-imaging and genetics project in the United States.

—Staff writer Risheng Xu may be reached at xu4@fas.harvard.edu.