This study investigated how antioxidants affect the cytotoxicity of phenolic phytochemicals, specifically epigallocatechin gallate (EGCG) and curcumin, on HCT116 colon cancer cells. Both compounds induced DNA damage and apoptosis in these cells. However, the presence of antioxidants like ascorbate and N-acetylcysteine (NAC) inhibited EGCG-induced DNA damage and apoptosis, but did