Safe, effective drug therapy in older adults requires an understanding of drug disposition and response in this population. Evidence suggests that physiologic changes during aging, including hepatic or renal function changes, contribute to pharmacokinetic differences. A major issue surrounding the study of older adults relates to the ability to study a large number of people in a minimally invasive way. Population pharmacokinetics provides a potential means of addressing this issue and a tool to evaluate drug exposure's magnitude and consistency. This article highlights examples of pharmacokinetic studies in psychiatry, in particular those conducted in older adults. It also reviews new drugs approved for treatment in psychiatry or neurology, many of which were developed as novel formulations (eg, extended-release transdermal film) with improved pharmacokinetic profiles or developed with regard to the actions of a specific enantiomer or metabolite.