Addiction is a brain disorder, not a lifestyle choice, a new study at the University of Cambridge suggests.
Researchers scanned the brains of 50 cocaine or crack addicts and their non-addicted siblings and compared them to those of 50 unrelated, healthy volunteers.
It was found that both the dependent and non-dependent siblings had the same abnormalities in the part of the brain associated with self-control.
The study, published in the journal Science, suggests that the brains of addicts may be "hard-wired" for addiction.
Lead researcher, Dr Karen Ersche of the Behavioural And Clinical Neuroscience Institute at Cambridge University, told The Huffington Post: "There has always been a stigma attached to addiction. What this study shows is that addiction is not a lifestyle choice or a failure of character but a brain disorder - and as such it should be treated like other psychiatric disorders."
The similarity between the brain scans of the addicts and their siblings supports the long-held belief that those with a family history of drug abuse have a higher risk of addiction.
However, what interests Dr Ersche is how some people with a genetic predisposition to addiction have the self-control to stay off drugs.
She said: "The siblings of the addicts have had the same struggles, same education and same nutrition. Learning from them could open up new ways to look at the problem."
Dr Ersche says the siblings of drug addicts, who have until now been largely ignored and hiding "in the shadows", could hold the key to learning more about the nature of addiction.
"The next step is to look into what has protected them, how their brains have compensated and to understand their resilience to addiction."
She adds: "We need to find out why some people become addicts rather than judging them."
Dr Paul Keedwell, a consultant psychiatrist at Cardiff University, told the BBC: "Addiction, like most psychiatric disorders, is the product of nature and nurture.
"We need to follow up people over time to quantify the relative risk of nature versus nurture."
He added: "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."