<p>Red yeast rice (RYR) is commonly used as colouring and flavouring agent in foods throughout East Asia. RYR contains monacolin K, a compound known to lower blood lipids level, which has led to its use as a health functional food in Korea. Additionally, RYR is frequently used as a food ingredient and is incorporated into processed foods such as bread and makgeolli, a traditional Korean alcoholic beverage. However adverse effects associated with RYR have been reported by several regulatory agencies, prompting the need for further investigation of its safety as a general food ingredient. To evaluate its safety, a 90-day feeding study was conducted using Sprague–Dawley (SD) rats, which were randomly assigned to three experimental groups. The experimental diets were prepared by replacing the corn starch in AIN 93G with RYR and/or white rice. Rats fed RYR showed lower body weight gain, accompanied by reduced food efficiency. No signs of toxicity were observed in serum clinical chemistry, relative organ weights, or histopathological analysis. However, hyperplasia and hypertrophy were observed in the thyroid, although the cause remained unclear. These results suggest that RYR exhibits a very low toxic potential, if any. Nevertheless, caution is advised regarding its expanded use, particularly among younger population, due to its growing inhibitory effects.</p>