Peroxidase catalyzes the breakdown of hydrogen peroxide into water and oxygen. This reaction happens naturally in many organisms. Horseradish and other plants contain peroxidase in abundance. Manufacturers sometimes add it to enzyme supplement blends, but the enzyme's role in human digestion remains unclear.
You will rarely find peroxidase as a standalone supplement. It mostly appears in green food formulas or broad-spectrum enzyme products. Within those blends, it is intended to back up the body's own antioxidant processes. Concrete evidence that supplemental peroxidase does anything specific for people is thin.
Safety data is missing because so little human research exists. Only use this or any unproven enzyme supplement under professional guidance.