Rewarding drugs produce taste avoidance, but not taste aversion

Paradoxically, drugs that animals will self-administer also produce conditioned taste avoidance at similar dosage levels. The present review presents evidence that the taste avoidance produced by these rewarding drugs differs qualitatively from the taste avoidance produced by the nonrewarding, emetic drug, lithium chloride. An analysis of data pooled across 6 experiments compares the nature of flavor-drug associations produced by various rewarding drugs (amphetamine, cocaine, methamphetamine, methylphenidate, morphine, nicotine and phencyclidine) with that produced by lithium. The data from the groups conditioned with the rewarding drugs and with lithium were combined into the two categories of low/moderate and high doses. When assessed by the CTA test, the rewarding drugs did not differ from lithium in the strength of the CTA at low/moderate or at high doses. However, when assessed by the TR test, lithium produced more prominent aversive taste reactions than did the rewarding drugs. These findings suggest that the flavor-drug association produced by lithium and rewarding drugs differs qualitatively. With the large pooled data set we also assessed the relationship among the various TR categories, resulting in two factors of "Ingestion" and "Aversion" accounting for 55% of the total variability within the data.