Neurometabolic mechanisms for memory enhancement and neuroprotection of methylene blueIt is also important to note that adverse effects of MB are not explained solely on the basis of hormesis or oxidative damage, but also on that of its chemical purity. Even pharmaceutical (USP) grade MB contains impurities, such as arsenic, aluminum, cadmium, mercury and lead. At low doses, the presence of contaminants is not of great concern, but at higher doses non-specific effects due to accumulation of various toxic and bioactive substances are possible. Industrial-grade and chemical-grade MB sold as a dye or stain can consist of more than 8% or 11% of various contaminants (NTP, 2008, Sigma Chemical Co, St. Louis, MO) and should not be administered to humans or animals. For example, commercial chemical suppliers routinely warn that their non-USP MB products are of a chemical grade not suitable for use in living applications. Nevertheless, some recent studies have used these impure chemical-grade MB products with living cells and animals, obtaining potentially misleading dose-response and toxic effects (Atamna et al., 2008; Auerbach et al., 2010)