Brain scans have revealed a possible biological basis for cocaine addiction which may explain why some get hooked, while others can use the drug socially.

The scans show cocaine alters parts of the brain controlling behaviour and appropriate decision-making.

In effect, the drug messes with what is colloquially known as willpower - with some maybe more vulnerable than others.

Trinity College Dublin researchers will present their findings to a Royal Society meeting.

The researchers took brain scans of cocaine users while they performed computer tasks.

They found that cocaine increased activity in areas of the pre-frontal cortex.

The scans also revealed differences in brain structures of cocaine users.

It is unclear whether the differences existed before they started taking cocaine, or were a result of using the drug.

But the findings raise the possibility that differences in brain structure render some people potentially more vulnerable to the effects of the drug.

Lead researcher Dr Hugh Garavan said previous research into drug abuse had tended to focus on the emotional aspects of addictions - such as pleasure seeking, craving and withdrawal.

The latest study suggests that it is not simply these emotions that are affected by cocaine, but the way the brain deals with them, and keeps them in check by controlling a person's actions.

Better treatment

He said: "This research helps us move away from thinking of drug dependence as a moral weakness and allows us to see it as more of a medical condition.

"Understanding the role that our brain plays in addiction may also have important implications for treating long-term addiction and designing intervention therapies.

"Importantly, new medication based on certain chemical processes in the brain could be developed as currently there are no good pharmacological treatments for cocaine.

"Traditional treatment therapy such as counselling or rehab could also be adapted to train addicts to monitor their behaviour and practice impulse control."

Dr Gerome Breen, of the Institute of Psychiatry, said: "We now know that the effects of cocaine on the brain are multi-facetted.

"Dr Garavan and his collaborators have shown convincingly that the brain regions controlling impulse control have their activity altered by cocaine.

"This aids in our understanding of cocaine's effects and, thus, the causes of cocaine addiction."