"My destructive side has grown a mile wide," she sang on her first album in 2003. The cause of Amy Winehouse's death has not yet been confirmed, but her struggles with drug addiction, and more recently alcoholism, mean most people will be shocked if a link isn't found.
But have you ever wondered why one person can drink like a fish for years and never become an alcoholic, while for others, like Winehouse, a tipple or 10 can begin the slide into dependency? Why can one person take that first disgusting drag of a cigarette (for that first drag is always disgusting) and say never again, while for others it becomes the start of nicotine dependence, still the most common addiction in the world?
It's a question that has dogged professionals for decades. So what have they discovered? While addiction is naturally associated with drink and drugs, is that the whole story? Can, as the NHS claims, anything be addictive, from gambling to chocolate?
Addiction has to start with exposure, says Dr Gillian Tober, president of the Society for the Study of Addiction. "It's generally for social reasons – groups of friends or a boyfriend or girlfriend – and it's often not pleasant. The reward is merely social. It then becomes reinforced and casual use shifts to dependence."
Drugs directly feed the reward circuitry of the brain, she says, and the brain learns to look forward to the thrill. Tolerance occurs as you demand more each time. Physiological dependence – addiction – then emerges. "It is this area – the mechanisms involved in the addictive process – where research has been most progressive and this has meant we have a lot more effective medications to help people come off nicotine, alcohol and opiates," Ilana Crome, a professor of addiction psychiatry at Keele University, says. "But we still don't know what actually causes addiction."
Indeed, many people drink but few are addicted. During the Vietnam war, when many American soldiers took lots of heroin, there were concerns that they would have difficulty coping without it when they came home. In fact, when they returned to an environment where there wasn't the same availability and it wasn't part of their social lives, most were fine. Likewise, when opiates have been given to cancer sufferers for many years, studies show that only a few remain addicted.
"There is no single reason why this is the case," Dr Tober says. "There are not even any particular personality characteristics that predispose people to becoming addicted. There are risks involved in being outgoing, but equally there are risks involved in being introverted. Every sort of personality can become addicted."
Indeed, a long-term study of 500 men, which began in the 1940s, exploring why some people become addicts while others don't, found there were no consistent personality types, says Bob Adams, a consultant psychiatrist in York NHS Trust.
But the Faculty of Addictions at the Royal College of Psychiatrists claims there are three key risk factors – biological, psychological and social. Biologically, addicts may be wired differently, particularly in the brain's orbito-frontal cortex, the part of the brain involved in weighing up the pros and cons of a particular action, they say.
Meanwhile, scientists at the Neurocentre Magendie in Bordeaux recently found those who became addicts had brains incapable of returning to normal after regular drug abuse. Long-term drug binges change the way people's minds work, but they only become addicts if their brain cannot bounce back to normal when they stop, the French study found. Addicts lose the ability to produce a form of brain plasticity, known as LTD, crucial for developing and holding new memories and therefore in having flexible behaviour, they concluded.
"Scandinavian studies have shown that children of alcoholics – even those who were adopted – are more likely to become alcoholics themselves, suggesting there is a genetic component," Dr William Shanahan, a lead addiction consultant at Capio Nightingale Hospital in London, says. "It doesn't mean you're going to see the addiction through – you still have free will, after all, so you might, for example, recognise it in others around you early on and get frightened off, or something else, like religion, acts as your salvation. In fact, it's often the case that if you find a non-drinker, you can usually find a drinker somewhere in their lives."
The second risk factor is psychological trauma. Childhood neglect, abuse or bereavement is extremely common among addicts, Harry Shapiro from DrugScope, says. For others, the trauma comes later – a bereavement, loss of job or late-onset anxiety might make them turn to the bottle or cocaine. Research from the Nineties found there may be a biological link here, too. Levels of feel-good chemicals in the brain, mainly serotonin and dopamine, can be reduced by any traumatic event such as divorce or abuse. People who become addicted to certain substances are subconsciously trying to boost the levels of these feel-good chemicals.
Thirdly, social risks include the availability of the particular drug, being around others that take it and social deprivation. "Most of the people who come forward for heroin or crack use are pretty impoverished," Shapiro says.
Dr Farrukh Alam, consultant psychiatrist and clinical director at Central and Northwest London NHS Foundation Trust, believes the clues that we have about these, and other, risk factors mean that we may be able to identify a propensity towards addiction. You can spot some traits as early as late adolescence, he says. "We know, for instance, that among those most prone are people with compulsive or impulsive types of behaviour, an unwillingness to take responsibility for their own actions or who are stressed and anxious even in times of relative ease. The age of initiation is relevant, too – the earlier you start to misuse substances, the more likely you are to develop chronic dependence." Certain occupations have also been shown to be higher risk – media, entertainment, catering and the military among them.
Some even believe there's an "addictive personality", seen in people who have an addictive edge, that obsessive side to their personality that gets them practising at something until they're the best. It would certainly explain why so many people famous for their talents – Andre Agassi, Paul Gascoigne, and Winehouse among them – wind up in rehab.
Most addiction professionals talk about drugs and alcohol, but can you become addicted to anything? Gambling is accepted as a behaviour involving a thrill that the brain can become hooked on. And the NHS is reconsidering sex addiction as a genuine disorder after the American Psychiatric Association added it to its main diagnostic manual.
But not everyone is convinced. "I think the addiction has become a lazy word for a bit of an obsessive habit, which is not the same," Shapiro says.
"Put it this way – how many people do you know whose job has gone out of the window or they have neglected everyone in their lives because they want to buy more shoes, get a better tan or eat more chocolate?"
How to tell if you're an addict If you answer yes to three or more of these, it is probably time to seek help:
* Do you crave the substance or behaviour?
* Do you have difficulty controlling your intake?
* Have you become tolerant to it – ie, you need increased amounts in order to produce the same effects?
* Do you neglect other interests to feed your habit?
* Do you get physiological withdrawal symptoms upon cessation, such as sweating, anxiety and tremors?
* Do you persist in its use despite understanding the harmful consequences?