There is a vast range in potency (>20,000-fold) of inducers of Nrf2 signaling used in cytoprotection studies. Optimal balance of potency, efficacy and specificity have not been defined in pre-clinical or clinical studies. Values in parentheses are the concentrations required to double NQO1 activity in Hepa1c1c7 cells. BHT, butylated hydroxytoluene; oltipraz, 5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione; sulforaphane, (−)-1-isothiocyanato-(4R)-(methylsulfinyl)butane; CDDO-Im, 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole. Figure adapted from Kensler et al. (2010).