This study investigated the chronic toxic effects of carrageenan on the thyroid gland and pancreas in rats and the possible protective effects of diacerein. Rats were divided into groups receiving carrageenan, diacerein, or a combination. Biochemical, histological and immunohistochemical analysis was performed after 3 months. Carrageenan significantly increased oxidative damage in the thyroid and decreased thyroid function markers compared to controls. Diacerein ameliorated these effects when given with carrageenan. Histologically, carrageenan caused hypothyroid changes while the combination caused milder changes. Carrageenan increased proliferating cell nuclear antigen expression in the thyroid, indicating oxidative damage, which was