A variety of natural products from plant sources, particularly flavonoids, have long been observed to have antioxidant activity with potential benefits for human health. Antioxidant triterpenes are less common. Celastrol is a triterpenoid antioxidant compound isolated from the Chinese thunder god vine (T. wilfordii). In an isolated rat liver assay of lipid peroxidation, celastrol had an IC50 value of 7 µM, equivalent to about 15 times the antioxidant potency of α-tocopherol.