Rat Park was a study into drug addiction conducted in the late 1970s (and published in 1981) by Canadian psychologist Bruce K. Alexander and his colleagues at Simon Fraser University in British Columbia, Canada.
Alexander's hypothesis was that drugs do not cause addiction, and that the apparent addiction to opiate drugs commonly observed in laboratory rats exposed to them is attributable to their living conditions, and not to any addictive property of the drug itself.
To test his hypothesis, Alexander built Rat Park, a large housing colony, 200 times the floor area of a standard laboratory cage. There were 16–20 rats of both sexes in residence, food, balls and wheels for play, and enough space for mating. The results of the experiment appeared to support his hypothesis.
The two major science journals, Science and Nature, rejected Alexander, Coambs, and Hadaway's first paper, which appeared instead in Psychopharmacology in 1978. The paper's publication initially attracted no response. Within a few years, Simon Fraser University withdrew Rat Park's funding.
Rat Park experiments
In Rat Park, the rats could drink a fluid from one of two drop dispensers, which automatically recorded how much each rat drank. One dispenser contained a morphine solution and the other plain tap water.
Alexander designed a number of experiments to test the rats' willingness to consume the morphine. The Seduction Experiment involved four groups of rats. Group CC was isolated in laboratory cages when they were weaned at 22 days of age, and lived there until the experiment ended at 80 days of age; Group PP was housed in Rat Park for the same period; Group CP was moved from laboratory cages to Rat Park at 65 days of age; and Group PC was moved out of Rat Park and into cages at 65 days of age.
The caged rats (Groups CC and PC) took to the morphine instantly, even with relatively little sweetener, with the caged males drinking 19 times more morphine than the Rat Park males in one of the experimental conditions. The rats in Rat Park resisted the morphine water. They would try it occasionally—with the females trying it more often than the males—but they showed a statistically significant preference for the plain water. He writes that the most interesting group was Group CP, the rats who were brought up in cages but moved to Rat Park before the experiment began. These animals rejected the morphine solution when it was stronger, but as it became sweeter and more dilute, they began to drink almost as much as the rats that had lived in cages throughout the experiment. They wanted the sweet water, he concluded, so long as it did not disrupt their normal social behavior. Even more significant, he writes, was that when he added a drug called Naloxone, which negates the effects of opioids, to the morphine-laced water, the Rat Park rats began to drink it.
In another experiment, he forced rats in ordinary lab cages to consume the morphine-laced solution for 57 days without other liquid available to drink. When they moved into Rat Park, they were allowed to choose between the morphine solution and plain water. They drank the plain water. He writes that they did show some signs of dependence. There were "some minor withdrawal signs, twitching, what have you, but there were none of the mythic seizures and sweats you so often hear about ..."
Alexander believes his experiments show that animal self-administration studies provide no empirical support for the theory of drug-induced addiction. "The intense appetite of isolated experimental animals for heroin in self-injection experiments tells us nothing about the responsiveness of normal animals and people to these drugs. Normal people can ignore heroin ... even when it is plentiful in their environment, and they can use these drugs with little likelihood of addiction ... Rats from Rat Park seem to be no less discriminating."
Reaction to the experiment
Further studies showed mixed results. One of those studies found that both caged and "park" rats showed a decreased preference for morphine, suggesting a genetic difference. Another found that while social isolation can influence levels of heroin self-administration, isolation is not a necessary condition for heroin or cocaine injections to be reinforcing.
Other studies reinforced the "Rat Park" findings showing that environmental enrichment reduced cocaine seeking behavior in mice  and that environmental enrichment can eliminate already established addiction-related behaviors. Furthermore, removing mice from enriched environments has been shown to increase vulnerability to cocaine addiction  and exposure to complex environments during early stages of life produce dramatic changes in the reward systems of the brain that result in reduced reactivity to drugs of abuse.
- Alexander, Bruce K., (2001) "The Myth of Drug-Induced Addiction", a paper delivered to the Canadian Senate, January 2001, retrieved December 12, 2004.
- Slater, Lauren. (2004) Opening Skinner's Box: Great Psychological Experiments of the Twentieth Century, W.W. Norton & Company.
- Alexander, B.K., Coambs, R.B., and Hadaway, P.F. (1978). "The effect of housing and gender on morphine self-administration in rats," Psychopharmacology, Vol 58, 175–179. PMID 98787
- Bruce Alexander's 2007 Sterling Prize acceptance speech. 2007. Event occurs at 1:05:15-1:10:00. Retrieved 2013-05-10.
- Petrie, B.F., Psychol Rep. 1996, 78, 391–400. PMID 9148292
- Bozarth MA, Murray A, Wise RA., Pharmacol Biochem Behav. 1989 Aug;33(4):903-7. PMID 2616610
- Chauvet, Claudia et al. “Environmental Enrichment Reduces Cocaine Seeking and Reinstatement Induced by Cues and Stress but Not by Cocaine.” Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology 34.13 (2009): 2767–2778. PMID 19741591
- Solinas et al."Reversal of cocaine addiction by environmental enrichment." Neuropsychopharmacology. 2009 Apr;34(5):1102-11. doi: 10.1038/npp.2008.51. PMID 18955698
- Nader, Joëlle et al. “Loss of Environmental Enrichment Increases Vulnerability to Cocaine Addiction.” Neuropsychopharmacology 37.7 (2012): 1579–1587. PMID 22334125
- Solinas, M et al. "Environmental enrichment during early stages of life reduces the behavioral, neurochemical, and molecular effects of cocaine." Neuropsychopharmacology. 2009 Apr;34(5):1102-11. doi: 10.1038/npp.2008.51 PMID 18463628
- Alexander, B.K., Beyerstein, B.L., Hadaway, P.F., and Coambs, R.B. (1981) "Effect of early and later colony housing on oral ingestion of morphine in rats," Pharmacology Biochemistry and Behavior, Vol 15, 4:571–576. PMID 7291261
- Alexander, B.K. (1985) "Drug use, dependence, and addiction at a British Columbia university: Good news and bad news," Canadian Journal of Higher Education, 15, 77–91.
- Alexander, B.K. (1987) "The disease and adaptive models of addiction: A framework evaluation," Journal of Drug Issues 17, pp. 47–66.
- Alexander, B.K. (1990) Peaceful measures: Canada's way out of the War on Drugs, Toronto University Press. ISBN 0-8020-6753-0
- Alexander, B.K. (2000) "The globalization of addiction," Addiction Research
- Drucker, E. (1998) "Drug Prohibition and Public Health," U.S. Public Health Service, Vol. 114
- Goldstein, A. Molecular and Cellular Aspects of the Drug Addictions. Springer-Verlag, 1990. ISBN 0-387-96827-X
- Goldstein, A.From Biology to Drug Policy, Oxford University Press, 2001. ISBN 0-19-514664-6
- Website of the U.S. Office of National Drug Control Policy
- Peele, Stanton. A discussion about addiction, archived link from July 7, 2004.
- MacBride, Katie (September 5, 2017). "This 38-year-old study is still spreading bad ideas about addiction". The Outline. Retrieved September 11, 2017.
- Much More Than A Drug Problem Bruce Alexanders lecture in Vancouver Institute 5.2.2011.
- Rat Park drug experiment cartoon – Stuart McMillen comics
- Rat Park and Other Children's Stories — The Orange Papers
- Neurobiology of addiction versus drug use driven by lack of choice
- Rat Water Bottles