evidence that the impoverished small cage environments that are standard for the housing of laboratory animals have undue influence on lab animal behavior and biology. These conditions can jeopardize both a basic premise of biomedical research—that healthy control animals are healthy—and the relevance of these kinds of animal studies to human conditions. Criticisms Replication Bruce Petrie (1996), a graduate student of Alexander's, attempted to replicate the study and correct for the original studies on 20 rats using two different methods for measuring morphine consumption between conditions (which introduced a potential confound). The study was not able to replicate the results, and the author suggested that strain differences between the rats Alexander's research group used could be the reason for this. There has been little subsequent interest in replicating the studies due to several methodological issues present in the originals. Issues included the small number of subjects used, the use of oral morphine, which does not mimic actual conditions of use (and introduces a confound because of the bitterness of morphine), and the measurement of morphine consumption, which differed between conditions. Other problems included equipment failures, lost data and rat deaths. However, some researchers have shown an interest in "conceptual" replication to continue exploring the contribution of environmental and social enrichment to addiction. Media interpretation Johann Hari, a journalist, gave a popular TED Talk about the results of the study. In it, he interpreted the studies to suggest that biological underpinnings are not the cause of addiction, instead shifting the etiology to a need for healthy relationships. The YouTube channel Kurzgesagt created and published a video based on Hari's book, which garnered over 19 million views. The channel later took down the video, stating that they improperly represented the evidence. Researchers have re-iterated that the results of Alexander's studies highlight issues with rat models kept in bare-bones lab environments, and help implicate the environment as a contributing factor to addiction. However, the media has overstated the studies' importance by suggesting it represents a paradigm shift in research, and that the environment is the only—or the key factor—in addiction. See also Effect of psychoactive drugs on animals References Further reading Alexander, B.K. (1990) Peaceful measures: Canada's way out of the War on Drugs, Toronto University Press. 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