Rat Park, a study of addiction

The rat colony was built to examine Alexander's hypothesis that drug addiction is a myth and that continued drug use, particularly the use of heroin, is largely the product of unhappiness, not neurophysiological compulsion. Alexander hypothesized that the addiction to morphine commonly observed in laboratory rats exposed to it is attributable to the conditions in which they are normally kept, and not to any addictive property of the drug itself.

Better surroundings, Alexander believed, would reduce or eliminate the apparent dependence. To test his hypothesis, he built Rat Park. It was 200 times the square footage of a standard laboratory cage. There was companionship, with 16–20 rats of both sexes in residence, an abundance of food, empty tins for burrowing, balls and wheels for play, a special space for mating, shavings for nesting, and a private place for giving birth. The results of the experiment appeared to support Alexander's hypothesis. The control group housed in the usual laboratory conditions consumed up to 20 times more morphine than the rats in Rat Park, and even those already addicted weaned themselves off the drug once moved there. They wanted to play, eat, and mate, Alexander concluded, not be anesthetized. "Nothing that we tried," he wrote, "instilled a strong appetite for morphine or produced anything that looked like addiction in rats that were housed in a reasonably normal environment."

Rat Park shows, he believes, that the "belief in drug-induced addiction, at least with respect to heroin and cocaine, has no status as empirical science, although it has not been disproven. It is believed for some reason other than its empirical support." Chemicals do not cause addiction "in the way that the measles virus causes a rash of red spots".