Drug addicts and their non-addicted siblings share certain features in the brain, suggesting a susceptibility to addiction is inherited but is also a flaw that can be overcome, scientists said on Thursday.

Researchers who scanned the brains of 50 pairs of brothers and sisters of whom one was a cocaine addict found that both siblings had brain abnormalities that make it more difficult for them to exercise self-control.

The findings increase understanding of why some people with a family history of drug abuse have a higher risk of addiction than others and could point to new treatments to help vulnerable people learn how take control before addictions set in.

"If we could get a handle on what makes unaffected relatives of addicts so resilient we might be able to prevent a lot of addiction from taking hold," said Paul Keedwell a consultant psychiatrist at Britain's Cardiff University, who was not involved in the research but was encouraged by its findings.

Good data on addiction is hard to gather since many drug abusers and alcoholics exist on the margins of society, but the World Health Organization estimates that at least 15.3 million people worldwide have drug use disorders. It says at least 148 countries report problems with injected drug use.

A study in the Lancet medical journal in January said that as many as 200 million people use illicit drugs worldwide each year, with use highest in wealthy countries.

Unhealthy addictions can also range from narcotics and prescription medicines to legal substances like cigarettes and alcohol and lifestyle factors such as over-eating or gambling.

Scientists have noticed brain differences in drug addicts before, but as yet they were not sure whether those differences came before the drug use, or were as a result of it.

Karen Ersche of the Behavioral and Clinical Neuroscience Institute at Britain's Cambridge University led a team of researchers who got around this problem by studying pairs of biological siblings - one addicted and one with no history of chronic drug or alcohol abuse - and comparing both siblings' brains to those of other healthy people.

Their results, published in the journal Science, showed that both addict and non-addict siblings shared the same abnormality in the parts of the brain linked to controlling behavior - regions known as the fronto-striatal systems.

"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," said Ersche.

"Our findings now shed light on why the risk of becoming addicted to drugs is increased in people with a family history:... Parts of their brains underlying self-control abilities work less efficiently.

Ersche said the next step would be to explore how the siblings who don't take drugs manage to overcome their brain abnormality, so scientists can better understand what protects them from drug abuse. This may provide vital clues for developing more effective therapies against addiction.

Asked to comment on the study, Derek Hill, a professor of Medical Imaging Science at University College London, said it was a "clearly designed" piece of research which showed that this sort of brain scanning might be used to find so-called biomarkers to help develop new treatments for other self-control-related conditions such as over-eating.

"Unfortunately, it takes years to develop an imaging method like this to the level of maturity needed to help develop new treatments, so practical benefits are some way in the future," he said.