ABSTRACT
Substance abusers frequently use multiple agents during the same day or week. These agents are sometimes from the same group of agents for which they have already developed tolerance and therefore they experience cross tolerance; or they may be from a totally different group of drugs. Not infrequently tolerance to two or more groups of drugs is present in the same individual. The makeup of an individual that leads to the use of one drug also produces a tendency to use other agents. Thus the majority of abusing subjects are also heavy ingestors of caffeine and use tobacco. Table 46 suggests some of the commonly encountered circumstances under which this happens.
