Tabriz University of Medical Sciences Advanced Pharmaceutical Bulletin 2228-5881 12 1 2022 01 01 Photosensitivity Reactions Induced by Photochemical Degradation of Drugs 77 85 10.34172/apb.2022.010 EN Hajnal Klelemen https://orcid.org/0000-0001-5043-3937 Gabriel Hancu https://orcid.org/0000-0003-2564-9271 Edina Kacsó Lajos-Attila Papp https://orcid.org/0000-0002-5633-0530 Journal Article 10.34172/apb.2022.010 2020 06 16 2021 05 28 Photochemical degradation of drugs can lead to degradation products with potential toxicor allergizing effects for the human body. A significant amount of work has been carried outover the past few decades to clarify the molecular mechanism of photosensitizing processesobserved after the administration of certain drugs and exposure to light. There is a closerelation between the photosensitizer effect of a drug and its chemical structure. Compoundspossessing certain moieties and functional groups in their molecular structure, like aromaticchromophore systems or photo-dissociable bonds that can form free radicals, and consequentlyare susceptible to have light-induced adverse effects. Photoionization, photodissociation,photoaddition and photoisomerization are the main chemical processes, which can occurduring the photochemical decomposition of a pharmaceutical compound. The current studyis a short review describing photochemical degradation of certain pharmaceuticals, presentingspecific examples from various pharmaceutical classes for the different types of decompositionmechanisms. In vivo methods and clinical tests available for the investigation of photosensitizingreactions are also discussed.