This article provides an overview of the state of the art in pharmaceutical applications of absorption spectroscopy and spectrofluorimetry in the analysis of phenothiazines by indirect method using peroxides. This review presents the fundamentals for the beginner and, for the expert, discusses both qualitative and quantitative analysis problems. Several sections focus on the determination of phenothiazines, in various matrices, the coupling of spectrophotometric methods, and the problems associated with the use of chemical reactions prior to spectrophotometric and spectrofluorimetric measurements. The final section provides a survey of the spectrophotometric and spectrofluorimetric determination of the main families of phenothiazines in the form of the corresponding sulfoxides obtained with peroxyacids as new analytical reagents, emphasizing the achievements of the last decade.