Chasing the Scream's Rat Park: The Replication Problem

Bruce Alexander and colleagues at Simon Fraser University ran the Rat Park studies in the late 1970s and published them between 1978 and 1981 (Alexander, Coambs and Hadaway, Psychopharmacology, 1978; Hadaway and colleagues, Psychopharmacology, 1979; Alexander and colleagues, Pharmacology Biochemistry and Behavior, 1981). Rats kept alone in standard cages drank more morphine solution than rats living together in a large open colony. Later attempts gave mixed results. Bozarth, Murray and Wise (1989) found that rats housed alone and rats housed in groups both learned to give themselves heroin and reached similar levels after a few weeks. Petrie (1996) could not repeat the housing difference: the isolated rats in his studies drank less than Alexander's had, and he suggested the supplier's rat strain had changed. The original result has not been reliably replicated, although the broader idea that surroundings can change drug taking still has support from other animal and human research. As Hari acknowledged in his corrections, a 1996 replication attempt did not reproduce Alexander's result. A 2019 commentary by Gage and Sumnall in Addiction argued the popular story has outrun the evidence. The specific claim that context almost completely overrides pharmacology is too strong: chronic opioid use produces lasting changes in the brain (Koob and Volkow, 2010).