Dibenzoazecines are a new class of potential neuroleptics with a high potential for the treatment of schizophrenia. Initial stress tests indicated that the lead compound, LE404, decomposes when exposed to oxygen and sunlight. In this follow-up study, the infuence of oxidative stress and photosensitivity was investigated in accordance with the ICH guidelines. These studies are of great importance for new APIs, as phototoxic and photoallergic reactions pose a signifcant risk to patients, especially with long-term medication, as it is not possible to completely avoid exposure to sunlight. Furthermore, the identifcation and prediction of the chemical lability of LE404 can be used to determine suitable storage conditions to prevent compound degradation. The efects of exposure of LE404 to a light source similar in spectrum and intensity to natural sunlight were investigated according to ICH-Q1B. Furthermore, the infuence of oxidizing agents was investigated under exclusion of light. Two degradation products were identifed. The extent and rate of degradation were continuously monitored using RP-HPLC–UV. Chromatographic separations were performed with a phenomenex™ Gemini 5 µm C18 (250 ×4.60 mm) column and acetonitrile/KH2PO4 bufer (4 mmol L−1, pH 2.5) as mobile phase at 220 nm. The photodegradation product was isolated using semi-preparative RP-HPLC. The oxidation product was obtained by quantitative conversion of LE404 in hydrogen peroxide and subsequent purifcation by preparative TLC. The structures of both degradation products were elucidated using HR-MS/MS, 1D- and 2D-NMR as well as FT-IR spectroscopy. The characterization of the degradation products serves as the basis for subsequent investigations into their toxicity.