Why do some people get addicted and others don't?
How come some folks can snort a line of coke and binge drink from time to time and then return to their normal lives, while others get hooked and destroy theirs?
We don't know the cause of Amy Winehouse's death - she joined the 27 Club last month - but she did have a lengthy public battle with substance abuse.
The question is why?
Addiction, it turns out, is both genetic and environmental. How it all shakes down seems to be a question of luck, opportunity, biology and coincidence.
"Certain personality types, like narcissists, are more vulnerable to addiction. Narcissism has been thought to develop in the first years of life, but I think you can also acquire it through great wealth and celebrity. People who fall prey to narcissism aren't able to assess what others are thinking. There are different paths to dependency: psychological, genetic, situational. Some people are vulnerable to the good feelings they get from various drugs, while others are less interested. Extremely wealthy people are at risk, as are the extremely poor. Those prone to dependency feel out of control; the drugs are an attempt to get control."
ROBERT MILLMAN, former director of the Drug and Alcohol Abuse Treatment and Research Service at New York-Presbyterian Hospital, New York
"Genetic and environmental causes each account for 50 per cent when it comes to addictions. That's not to say that's the ratio in any given individual. Some people have a genetic proclivity. Their brain falls in love with a particular substance. You are genetically coded for what drugs you are susceptible to. If you can keep potentially addicted brains away from drugs until those individuals are in their 20s, the incidence of addiction will go down. Addiction is a treatable disease, but like diabetes it requires attention, because it can be chronic. There are drugs that can help, but the problem with Naltrexone, for instance, is that we don't know who it will and won't work for."
DAVID WITHERS, MD, associate medical director, Marworth Treatment Center, Waverly, Pennsylvania
"There are behaviours that are voluntary and those that are involuntary. And what we mean by disease is symptoms that are involuntary. The question of whether addiction is a disease is determined by whether people classified as addicts are sensitive to drug-taking consequences. There's a consensus that an addict's drug use changes according to repercussions - whether or not they have children, whether there are legal sanctions, whether it threatens their income. Most people quit on their own in their late 20s, early 30s."
GENE HEYMAN, author, Addiction: A Disorder Of Choice; lecturer, Boston College, Harvard Medical School
"Think of stacks of Swiss cheese slices, with holes in different areas. One slice represents biology, one parenting style, one the neighbourhood, and so on. The holes represent risks, like a bad gene or bad maternal care. The holes need to be properly aligned for full-blown addiction. You may have genes that make you a novelty seeker, but if you're in a neighbourhood where drugs aren't available, you may not use. This is why addiction doesn't affect everybody. Just as it's difficult to predict who will get into it, it's hard to predict who will get out of it with different approaches. We're moving into personalized treatments based on life experience and genetics."
RUBEN BALER, health scientist administrator, National Institute on Drug Abuse, Bethesda, Maryland
"About 1 to 2 per cent of rock and pop stars die within five years of becoming famous. For those who don't, for a period of around 25 years after their success their levels of mortality are about double those of the general population. Causes of death are more greatly associated with alcohol and substance use. Part of it is opportunity and access. They're in an environment where there's easy access to drugs, where price isn't a problem, where they feel relatively protected."
MARK BELLIS, professor of public health, Liverpool John Moores University, Liverpool, England