Mechanisms of Drug Addiction
to the editor: Camí and Farré (Sept. 4 issue)1 pro- the authors reply: Dr. Munzar states that the data
vide a comprehensive review of the neuronaland behavioral mechanisms involved in drug addiction. Their information on the potential for abuse of cannabinoids, however, is outdated. The authors claim that, in contrast to results obtained withopioids, cocaine, amphetamines, ethanol, and nicotine, “laboratory animals cannot be taught to self-administer ∆9-tetrahydrocannabinol.” It has been shown that persistent self-administration behavior ismaintained with intravenous ∆9-tetrahydrocannabinol in animals, with patterns similar to those reported for cocaine given at doses comparable to those present in marijuana smoke inhaled by humans.2Justinova and colleagues recently demonstrated that even animals that have not previously been exposed to other psychoactive drugs can be taught to self-administer ∆9-tetrahydrocannabinol.3 Thosereports suggest that marijuana has as much potential for abuse as other drugs of abuse. It does not necessarily mean that the health or social consequences of marijuana use are similar to those of cocaineor heroin use or that marijuana has no therapeutic potential. The addictive properties of ∆9-tetrahydrocannabinol and other abused drugs, however, appear to be similar. Patrik Munzar, M.D.
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1. Camí J, Farré M. Drug addiction. N Engl J Med 2003;349:975-
we cite in our review regarding the potential for abuse of cannabinoids areoutdated. His argument is based on two previous experimental studies in which squirrel monkeys self-administered ∆9-tetrahydrocannabinol by the intravenous route. However, the evidence provided by Tanda etal.1 was not obtained from naive animals: the authors reported maintenance of ∆9-tetrahydrocannabinol selfadministration in four monkeys previously trained to self-administer cocaine. Previous...