The researchers scanned the brains of 50 pairs of brothers and sisters, one of whom was a cocaine addict and found that both the siblings had the same abnormality in a region of the brain known as fronto-striatal systems, which is associated with controlling behavior.
The researchers said that their study can shed light on why the risk of addiction is higher among people who have a family history of such addictions.
"It has long been known that not everyone who takes drugs becomes addicted, and that people at risk of drug dependence typically have deficits in self-control. Our findings now shed light on why the risk of becoming addicted to drugs is increased in people with a family history", lead researcher Dr Karen Ersche said.
The study has been published in the journal Science.