THE STIMULUS PROPERTIES OF 2 COMMON OVER-THE-COUNTER DRUG MIXTURES - DEXTROMETHORPHAN PLUS EPHEDRINE AND DEXTROMETHORPHAN PLUS DIPHENHYDRAMINE

Two groups of rats were trained in a two-choice drug discrimination pr ocedure under a fixed-ratio 10 schedule of food reinforcement. One gro up of rats (n=12) was trained to discriminate the presence and absence of a drug mixture containing 10 mg/kg dextromethorphan + 10 mg/kg dip henhydramine. The other group of rats (n=12) was trained to discrimina te the presence and absence of another drug mixture containing 10 mg/k g dextromethorphan + 10 mg/kg ephedrine. cross-generalization tests co nducted with each of the stimulus elements demonstrated that (1) the d rug mixtures were not perceived as new entities distinct from their co mponent elements and (2) the stimulus element saliency may be a factor : determining the nature of discriminative control by drug mixtures. C ross-generalization tests conducted with the psychomotor stimulants, c ocaine and amphetamine, engendered complete generalization to the trai ning cues in both groups, whereas, pentobarbital engendered predominan tly saline-or default-lever responding. These data suggest a potential abuse liability for both of these common over-the-counter drug mixtur es and cautions against the use of such combinations in pediatric pati ents.