pies may still have some desire to use drugs for at least five reasons. First, as Pentel (this volume) has described, immunotherapies only partially block the transport of drug molecules into the brain. Second, effectiveness will vary over time, so that a treatment that is completely effective at one time may be ineffective at another time. Third, adherence rates for a wide range of treatment regimens have been far from perfect (not necessarily through any fault of the providers) (McLellan et al., 2000), Fourth, it is not completely clear how immunotherapies and sustained-release formulations affect drug craving (Pentel, this volume). Fifth, psychopharmacologic effects are not the sole motive for drug use (Kosten and Kranzler, this volume).

It is likely that some or even many people given immunotherapies or sustained-release formulations of opioid blockers will continue to have some desire or craving to take drugs. Moreover, for some individuals, drug-taking may still have some effect on their brain (including cognition, reward pathways, and other effects). These individuals can be thought of as having received some fraction of the benefits of a 100 percent effective blocking of the drug, yet partial effects may be better than no effects at all. Individuals might continue to ingest some of the drug, but less than they otherwise would have and, hence, they and society generally would benefit. Another possibility, however, is that these individuals will try to swamp or override the partial blockade of the drug by ingesting larger doses than they would have in the absence of the immunotherapy or depot medication, resulting in greater total use than before treatment.

This perverse outcome is not implausible. To caricature, if using an immunotherapy meant that twice as much of the drug had to be ingested to get the same effect, from a drug consumer’s point of view that may be equivalent to a doubling of the price of a drug. In either event (a 50 percent effective immunotherapy or a price doubling), the user would have to spend twice as much to get the “same” brain reward. The critical question is how clients in treatment who receive these medications respond to different degrees of effectiveness, individually and on average. It is quite likely that some users will periodically attempt to swamp or override the medications at any level of effectiveness.

From an economic perspective, the responsiveness of consumers to price changes (or in this case, to medication effectiveness) can be summarized as the price elasticity of demand (MacCoun, this volume). In general, when prices increase (medication effectiveness increases) the amount of a commodity purchased decreases. When the price increases, the total amount spent on the commodity may decline, remain the same, or actually increase, depending on the nature and degree of change in consumption. The total amount spent on a commodity increases if the proportional



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