<p>The color and shape of the tablets manufactured by pharmaceutical companies were selected with branding and anti-counterfeiting measures in mind. Our previous report clarified that the discoloration of tablets by light exposure is due to the degradation of hydroxypropyl methylcellulose in the coating film and that the degradation reaction is triggered by TiO₂. In this study, we identified a pharmaceutical excipient that prevents light-induced discoloration of the coating film mediated by TiO₂. Among the excipients examined, triethyl citrate and glycerol triacetate, which are used as plasticizers, prevented color changes in the tablets. The prevention of color change was attributed to increased tensile strength rather than the coating film's glassy or rubbery state. In conclusion, the color change of tablets owing to photochemical reactions with TiO2 can be prevented by using excipients which can increase the strength of the coating film.</p> Graphical Abstract <p></p>