The predominant model of drug addiction views it as a disease: humans and animals will use heroin or cocaine for as long as they are available. When the drugs run out, they will seek a fresh supply; the drugs, not the users, are in control.

These conclusions, repeated frequently by politicians and the media, are based on experiments carried out almost exclusively on animals, usually rats and monkeys, housed in metal cages and experiencing a particularly poor quality of life. What would happen, wondered psychologist Dr Bruce Alexander, then of British Columbia's Simon Fraser University, if these animals were instead provided with a comfortable, stimulating environment?

In 1981, Alexander built a 200sq ft home for lab rats. Rat Park, as it became known, was kept clean and temperate, while the rats were supplied with plenty of food and toys, along with places to dig, rest and mate. Alexander even painted the walls with a soothing natural backdrop of lakes and trees. He then installed two drips, one containing a morphine solution, the other plain water. This was rat heaven: but would happy rats develop morphine habits?

Try as he might, Alexander could not make junkies out of his rats. Even after being force-fed morphine for two months, when given the option, they chose plain water, despite experiencing mild withdrawal symptoms. He laced the morphine with sugar, but still they ignored it. Only when he added Naloxone, an opiate inhibitor, to the sugared morphine water, did they drink it.

Alexander simultaneously monitored rats kept in "normal" lab conditions: they consistently chose the morphine drip over plain water, sometimes consuming 16-20 times more than the Rat Parkers.

Alexander's findings - that deprived rats seek solace in opiates, while contented rats avoid them - dramatically contradict our currently held beliefs about addiction. So, how might society benefit if his results were applied to human addicts? Nobody seemed to care.

Rejected by Science and Nature, Alexander's paper was published in the obscure Pharmacology, Biochemistry and Behavior, where it was summarily ignored.

Two decades later, Rat Park sits empty; addiction remains a disease and the war on drugs continues.