A 47-year-old woman developed severe kidney dysfunction after taking a lipid-lowering supplement, Red Yeast Rice Cholestehelp, for approximately 7 months. She experienced sudden nausea and an elevated serum creatinine level of 4.26 mg/dL. A kidney biopsy revealed findings consistent with acute tubular necrosis. Kidney function improved with discontinuation of the supplement and corticosteroid therapy. This case highlights the need for public awareness and warnings about the health risks associated with unregulated supplements, particularly in Japan, where similar cases have been reported. An investigation into the nephrotoxic ingredients in the same product batches is ongoing. The report underscores the importance of regulatory oversight and consumer education to prevent further adverse events.A 47-year-old woman developed severe kidney dysfunction after taking a lipid-lowering supplement, Red Yeast Rice Cholestehelp, for approximately 7 months. She experienced sudden nausea and an elevated serum creatinine level of 4.26 mg/dL. A kidney biopsy revealed findings consistent with acute tubular necrosis. Kidney function improved with discontinuation of the supplement and corticosteroid therapy. This case highlights the need for public awareness and warnings about the health risks associated with unregulated supplements, particularly in Japan, where similar cases have been reported. An investigation into the nephrotoxic ingredients in the same product batches is ongoing. The report underscores the importance of regulatory oversight and consumer education to prevent further adverse events.