Chronic, painful diseases such as endometriosis can lead to a severe reduction in the quality of life of those affected. Drug delivery systems, such as chitosan-containing hydrogels, could enable efficient pain management with prolonged and targeted drug release. Therefore, in the study presented here, hydrogels made of chitosan and the vanillin derivative 2-hydroxy-5-nitrobenzaldehyde were investigated as a drug delivery system for diclofenac sodium salt.