Conditioned opponent processes in the development of tolerance to psychoactive drugs

1. Tolerance may involve classical conditioning processes. A conditioned drug-opponent response is thought to increase with drug exposures and summate with the unconditioned response to the drug - resulting in tolerance. 2. Support for this theory comes from reports that tolerance exhibits many basic features of classical conditioning phenomena. 3. Problems for this account of tolerance arise from the fact that some, but not all, empirical attempts to demonstrate conditioned opponent responses have failed. 4. It has consequently been suggested that tolerance might best be conceptualised in terms of theories of habituation, which do not involve opponent processes. 5. The controversy over the role of opponent processes is theoretically important, because conditioned opponent processes are believed to be involved in dependence. Resolution of the controversy requires that parametric studies are conducted, in which the optimal conditions for obtaining conditioned tolerance are defined, and an efficient "model system" developed for analysis of the possible role of opponent processes in tolerance. 6. Research in this area highlights the importance of interdisciplinary studies of tolerance and dependence.