Discriminative stimulus effects of hallucinogens and psychostimulants in S(+)‐MDMA, and R(−)‐MDMA trained mice

3,4‐Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative with increasingly widespread abuse. MDMA has been difficult to classify as a stimulant or hallucinogen because it shares effects with both drug classes. Furthermore, racemic MDMA is composed of two isomers that vary in terms of behavioral effects rather than simple potency differences. Specifically, the R(−) isomer of MDMA has hallucinogen like effects whereas the S(+) isomer has stimulant like effects. In the present study, mice were trained under a liquid food reinforcer two lever operant paradigm to discriminate S(+) or R(−)‐MDMA from vehicle. Drugs that are hallucinogen like and either structurally similar (2,5‐dimethoxy‐4‐(n)‐propylthiophenethylamine ‐ 2C‐T‐7) or not (N,N‐Dipropyltryptamine ‐ DPT) and drugs that are stimulant like and either structurally similar (Amphetamine) or not (Cocaine) were substituted for the training drug in mice trained to discriminate each isomer. Within chemical class we have found apparent efficacy differences whereas within behavioral class we have found potency differences. These studies enlighten our understanding of the complex nature of the discriminative stimulus properties of MDMA.