Pharmaceutical companies assessing the nervous system effects of candidate therapeutics often use a behavioral assay in rodents that assesses the drug's subjective (internal stimulus) effects. Variants of this so-called "drug discrimination task" have also been widely used by basic scientist for more than 50 years to study the receptor actions of a host of ligands related to disease states and neuropathologies. Notably, most published research with this task has used male rats or mice. This situation is unfortunate and severely limits the utility of the research, given the well-documented differences between women and men on drug efficacy and safety, as well as known sex differences in the neural and behavioral effects of drugs. In this Viewpoint, we highlight the need for basic researchers, as well as pharmaceutical scientists, to include females in drug discrimination studies in a manner that allows detection and interpretation of potential sex differences.