Chasing the Scream: The First and Last Days of the War on Drugs

by Johann Hari

But when Bruce looked at these experiments, he noticed something. These rats had been put in an empty cage. They were all alone, with no toys, and no activities, and no friends. There was nothing for them to do but to take the drug. What, he wondered, if the experiment was run differently? With a few of his colleagues, he built two sets of homes for laboratory rats. In the first home, they lived as they had in the original experiments, in solitary confinement, isolated except for their fix. But then he built a second home: a paradise for rats. Within its plywood walls, it contained everything a rat could want—there were wheels and colored balls and the best food, and other rats to hang out with and have sex with. He called it Rat Park. In these experiments, both sets of rats had access to a pair of drinking bottles. The first bottle contained only water. The other bottle contained morphine—an opiate that rats process in a similar way to humans and that behaves just like heroin when it enters their brains. At the end of each day, Bruce or a member of his team would weigh the bottles to see how much the rats had chosen to take opiates, and how much they had chosen to stay sober. What they discovered was startling. It turned out that the rats in isolated cages used up to 25 milligrams of morphine a day, as in the earlier experiments. But the rats in the happy cages used hardly any morphine at all—less than 5 milligrams.