In the search for causes of human disease and variability of drug response, the study of interindividual differences in RNA processing has lagged substantially behind analyses at the DNA level. This chapter focuses on the post-transcriptional processes of RNA editing and alternative splicing. It considers the contribution of aberrations within these events to the efficacy of pharmacotherapy for psychiatric diseases. Specific examples of RNA processing defects within receptors for various neurotransmitters such as dopamine, glutamate, and serotonin are presented. In addition, mechanisms involved in the regulation of RNA editing and splicing are addressed as contributors to disease etiology and treatment. The chapter focuses on A-to-I editing and its role in the processing of several RNA transcripts in the central nervous system, including glutamate receptor subunits, the serotonin (5-HT) 2C receptor (5-HT2CR), and one of the enzymes catalyzing A-to-I modifications, adenosine deaminase (ADA), which acts on RNA 2 (or ADAR2).