One of the ways this theory was first established is through rat experiments - ones that were injected into the American psyche in the 1980s, in a famous advert by the Partnership for a Drug-Free America. You may remember it. The experiment is simple. Put a rat in a cage, alone, with two water bottles. One is just water. The other is water laced with heroin or cocaine. Almost every time you run this experiment, the rat will become obsessed with the drugged water, and keep coming back for more and more, until it kills itself.
The advert explains: "Only one drug is so addictive, nine out of ten laboratory rats will use it. And use it. And use it. Until dead. It's called cocaine. And it can do the same thing to you."
But in the 1970s, a Professor of Psychology in Vancouver called Bruce Alexander noticed something odd about this experiment. The rat is put in the cage all alone. It has nothing to do but take the drugs. What would happen, he wondered, if we tried this differently? So Professor Alexander built Rat Park. It is a lush cage where the rats would have colored balls and the best rat-food and tunnels to scamper down and plenty of friends: everything a rat about town could want. What, Alexander wanted to know, will happen then?
In Rat Park, all the rats obviously tried both water bottles, because they didn't know what was in them. But what happened next was startling.
The rats with good lives didn't like the drugged water. They mostly shunned it, consuming less than a quarter of the drugs the isolated rats used. None of them died. While all the rats who were alone and unhappy became heavy users, none of the rats who had a happy environment did.
At first, I thought this was merely a quirk of rats, until I discovered that there was - at the same time as the Rat Park experiment - a helpful human equivalent taking place. It was called the Vietnam War. Time magazine reported using heroin was "as common as chewing gum" among U.S. soldiers , and there is solid evidence to back this up: some 20 percent of U.S. soldiers had become addicted to heroin there, according to a study published in the Archives of General Psychiatry. Many people were understandably terrified: they believed a huge number of addicts were about the head home when the war ended.
But in fact, some 95 percent of the addicted soldiers - according to the same study - simply stopped. Very few had rehab. They shifted from a terrifying cage back to a pleasant one, so didn't want the drug any more.
