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discussed below, in order to measure dependence on different substances (for opiate users see Sutherland et al. 1986, specifically for heroin users see Strang et al. 1999 and Gossop et al. 1992, for cannabis users see Swift et al. 1998, for amphetamine users see Topp and Darke 1997; Topp and Mattick 1997a and Churchill et al. 1993, for benzodiazepine users see Ross et al. 1996, for cocaine users see Gossop et al. 1994). To date such measures have not been used to compare severity of dependence between substances, though the SDS has been used to compare severity across different methods of use of a substance (Strang et al. 1998, Gossop et al. 1994). The question of how dependence itself changes, though alluded to by Polich and his colleagues with reference to change in the severity of symptoms (Polich et al. 1981), does not appear to have been the focus of investigation.
1.6 A psychological explanation
At the time of the description of the drug dependence syndrome (Edwards et al. 1982), which was an adaptation of the idea of alcohol dependence syndrome to other drugs, tolerance and withdrawal symptoms were seen to be essential components of the syndrome, but as dependence on cocaine and amphetamine with their withdrawal like effects, sometimes referred to as rebound effects, were increasingly recognised, greater emphasis in research was placed upon the pursuit of relief or avoidance of these effects rather than the occurrence of the withdrawal phenomena themselves (Topp and Mattick 1997b).
During the eighties, the question of whether alcohol dependence and other drug dependence were the same, similar or separate phenomena was addressed. In many respects the phenomena had come to be seen as essentially the same (Edwards et al. 1982). However, difficulties arise if the features of tolerance and withdrawal are to be retained as part of the essence of dependence in that clearly these phenomena would vary with different drugs and with some drugs there seemed little evidence for their existence (Bryant et al. 1991). In order to resolve the difficulty with reference, for example, to cocaine, where objectively identifiable withdrawal symptoms were not manifest and yet cocaine seeking behaviour could be observed to have compulsive characteristics in the face of adverse consequences, a distinction was drawn between ‘psychological’ and ‘physical’ dependence. Edwards and his colleagues (1982) argued that this distinction caused unnecessary confusion and proposed the idea that tolerance and withdrawal might usefully be seen as separate phenomena from dependence referring to them instead as neuroadaptation.
It was as a result of clinical observations of the commonalities in dependent behaviour with 18