Variations on drug discrimination procedures were examined for their ability to reduce time needed for rats to acquire stimulus discrimination in a 3-choice drug-discrimination procedure. 1.5 mg/kg MDMA and 1 mg/kg D-amphetamine served as stimuli in the first study, and 0.08 mg/kg LSD and 1.5 mg/kg MDMA served as stimuli in the second study. Achievement of drug discrimination and time needed to achieve appropriate responding served as dependent measures in both studies, with 80% or more responses on the correct lever deemed successful acquisition of drug discrimination. In Study 1, rats were either trained by pairing a specific food reinforcer with a specific drug (i.e. plain sweetened milk with MDMA, chocolate sweetened milk with D-amphetamine and water with saline), or by randomly providing both reinforcers on correct lever press. The authors refer to the drug-reinforcer pairing as utilizing the differential outcome effect (DOE). In the second study, cues preceding food delivery (tones or lights) were either varied randomly or paired with a specific training drug, with the procedure using cue-drug pairing referred to as the differential outcome procedure (DOP). Findings were similar in both studies. Rats in the DOE condition and rats in the randomly paired rewards condition both successfully distinguished MDMA from D-amphetamine and saline. Likewise, rats in both the DOP and random-cue conditions successfully discriminated between MDMA, LSD and saline. The use of differential outcome effects or differential outcome procedures did not significantly reduce time needed to learn stimulus differentiation in a 3-lever drug discrimination paradigm. The authors conclude that these differential outcome procedures offer no advantages in learning different interoceptive (inside the organism) cues, even if they might prove advantageous in learning differences in exteroceptive (external to organism) variables.