[Drug discrimination: methodology and current problems].

The purpose of the drug discrimination experiments is, 1) quantitative description of the stimulus properties of drugs, and 2) qualitative description of the stimulus properties, that is, specification of the site of action (central vs peripheral), identification of substance carrying the stimulus property (the drug itself or its metabolites), measurement of similarity to other drugs, and antagonism of the stimulus properties. Feature of drugs as a discriminative stimulus is, 1) change of dose does not mean monotonic change of intensity, that is, different dose may result in different subjective quality, and 2) some drug seems to be a compound stimulus consisting of different stimulus properties, and asymmetric generalization between two drugs and individual differences in generalization tests can be explained in terms of selective stimulus control by different stimulus elements in the compound stimulus. Tolerance, species difference and relationships between the stimulus properties and other drug effects were also discussed.