Recent analytical advancements for sedative drug monitoring are a major topic in modern clinical stages. The liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) technique has been used for conventional therapeutic drug monitoring in the clinical stages. From the middle and late-2000s, LC-MS/MS with an electrospray ionization (ESI) interface has played an important role in pharmacokinetics, drug monitoring and metabolism studies since its introduction to the pharmaceutical industry and laboratory. Obviously, clinical researchers have needed highly sensitive, selective and accurate techniques for the sedative drug monitoring in various clinical stages. We review the current developments and reports regarding the application of LC-MS/MS with an ESI interface for sedative drug monitoring in the clinical stage.