Individuals with intellectual and developmental disabilities are often prescribed psychotropic medication to treat behaviors such as aggression and self-injury. Evaluation of these medications is often based on caregiver report or changes in frequency of behavior. The purpose of this research was to characterize the rate and function of problem behavior within an analogue functional analysis for three individuals diagnosed with autism as they experienced psychotropic medication changes. Results revealed that problem behavior, in terms of rate and function, were different across the various drugs prescribed. These data suggest that medication changes did not only produce changes in the rate of behavior but also in its function; that is, in behavioral parlance, medications can become motivating operations. This finding is lending support for the usefulness of conducting functional assessments throughout psychotropic medication changes. The importance of monitoring functional changes of target behavior is that concurrent behavioral interventions may have to be adjusted in accordance with those altered functional properties. Recommendations regarding future directions for research and implications of this line of research for treatment are discussed. (Contains 2 figures.)