“Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient conditions, which can lead to changes in its bioavailability. In this study, the kinetics of the pseudopolymorphic transitions of niclosamide crystals are characterized. FT-Raman spectroscopy is used to quantify the anhydrate and hydrate forms of niclosamide crystals, mostly because of its high sensitivity to the strong intermolecular interactions present in these systems. The samples are exposed to well-characterized relative humidity (RH) conditions during different periods of time and both water diffusion and polymorphic changes are monitored from the corresponding changes observed in the vibrational spectra. Both hydration and dehydration were found to be single-step processes, with a half-life time of ca. 142 and 63 h,respectively, at 24 °C.”