ABSTRACT
Tolerance is operationally defined as a decrease in the effectiveness of a drug given previous exposure to the drug. As a result, higher doses of the drug are required to produce a particular behavioral or physiological effect and previously effective doses lose some of their effectiveness. When the ability of a range of doses of a drug to produce a particular effect is measured, both before and after some exposure regimen, tolerance can be revealed by a shift to the right in the dose-effect function (i.e., the drug becomes less potent). Conversely, sensitization is operationally defined as an increase in the effectiveness of a drug given previous exposure to the drug. us, the effects of a particular dose of a drug become larger, and now lower doses of the drug may be sufficient to produce the target behavioral or physiological effect. When the ability of a range of doses of a drug to produce a particular effect is measured, sensitization can be revealed as a shift to the left in the dose-effect function (i.e., the drug becomes more potent). So, tolerance and sensitization are phenomena most often revealed by a change in drug potency that is attributable to previous exposure to the drug.
