By this time, you've probably heard of the death of Amy Winehouse. Though as of this writing the cause of death is unknown, most speculate (probably accurately) that her drug addiction was the cause or at least played a major part, and many say that they are "not all that surprised" or that they "saw this coming". There are a whole host of psychological theories this makes me think of, but that's not really what I want to speculate about at the moment.
Many find it difficult to understand how addiction can take over one's life as it did Amy Winehouse's life. There are a lot of people who argue that some have a genetic predisposition to develop addictions. It's true that there is some evidence that certain people have a predisposition to depression or anxiety that may relate to propensity to develop addictions. I think we're attracted to these explanations, not just because there is some evidence to support them, but because they give us a reason to believe "That would never happen to me."
As a social psychologist, though, I hesitate to depend too much on these explanations, because I know how powerful the situation can be. And as a (semi-recovered) behaviorist, I often think of how nearly anyone could be shaped and rewarded into developing an addiction. True, I don't want to go so far as some behaviorists, who firmly believed they could take any person and shape him or her to be anything (beggar, thief, etc.) regardless of their inherent talents (there's a good reason they made some of these arguments but that's a post for another day). At the same time, people respond to rewards and punishments, and some actions may feel so rewarding that we continue to engage in them, even if they are slowly killing us.
To put things simply, there is evidence that we have in our brains a "reward pathway" - connections within the brain that cause certain areas to "light up" when we experience something pleasurable; the areas that light up are associated with feelings of pleasure as well as with goal-directed behavior and motivation. (Learn more about it here.) That pathway not only allows us to say, at a neuronal level, "That feels good", but also, "I want to get more of that." We feel motivated to obtain more of that good feeling. Provided something pleasurable isn't (either accidentally or on purpose) combined with something unpleasurable, we're likely to try to obtain that good feeling again. For example, say you tried a really tasty food for the first time - such as chocolate cake (one of my favorites). If you tried the food, found it tasty, and didn't get sick afterward, you'd be really likely to eat that food again. If, on the other hand, you tried chocolate cake for the first time and got horribly ill afterward, whether it be "on purpose" (you discover you're allergic to chocolate) or "by accident" (you become ill from an unrelated sickness), you'd be motivated to avoid chocolate cake after that (and perhaps even avoid chocolate completely). Pretty much everyone has some experience like this - where you tried a new food and got sick afterward, so you avoid that food completely. We call this a "conditioned taste aversion".
Now, how does this relate to drug addiction? Let's say you tried a drug for the first time. If it felt really good and you didn't have any awful side effects occur soon after, you'd probably be motivated to try it out again. Over time, your positive associations with the drug become stronger and stronger, as do the connections to parts of the brain responsible for goal-driven behavior. A lot of people argue that drug addicts are lazy - actually, they're quite motivated, but their motivation is directed at getting their next fix. Humans in general are quite motivated to obtain things that feel good (which explains a lot of our maladaptive behaviors). Factor in the unpleasant withdrawal symptoms (that essentially punish the person for trying to quit using the drug), and you can see why someone would keep using.
Sadly, not everyone suffering from drug addiction has a family who wants to help them, but even people who have social support may not be able to beat the addiction. Amy Winehouse's father has been especially vocal about how much he wanted to help his daughter beat her addiction. For some people, a loving supportive family can, thankfully, get them out of the downward spiral. Unfortunately, depending on the drug of choice and many variables (too numerous to name here), the motivation to get more of that drug-enhanced happy feeling may be stronger than the motivation to please their family.
By no means am I excusing or condoning this behavior. The best way to avoid these problems is obviously to never start, and we need to keep working to find ways to keep people from trying drugs to begin with (if only programs like 'Just Say No' and 'DARE' actually worked, but a lot of research evidence says they don't). But if someone does begin using drugs, we have to keep in mind the powerful physical and psychological forces at work that make it difficult to quit, and we have to design detoxification and rehabilitation that take into account these forces.
As a celebrity, Amy Winehouse certainly had other forces at work and influences in her life that probably contributed to her addiction. Even so, the forces I've discussed above were definitely operating as well. Hopefully I've given you some food for thought; feel free to share in the comments below.