In the present study we investigated irritation of the oral mucosa and the safety of gummi drugs containing acetaminophen (AAP). The oral mucosae of hamsters were macroscopically examined for any evidence of irritation after gummi drugs were inserted into the cheek pouch and left there for 1 h. The cheek pouch tissue was also macroscopically and microscopically examined 24 h after gummi drugs were withdrawn from the cheek pouch. As a result, no evidence of irritation was found macroscopically 1 h after insertion, or macroscopically and microscopically 24 h after the withdrawal of the gummi drugs or placebos as compared with negative controls (saline). Considering these results, the gummi drugs administered in the present study produced no irritation to the oral mucosa.