The main classes of compounds possessing important anti-enzymatic properties in the prevention and protection against AD are the isoquinolines (especially the galantamine, protoberberine, aporphine, and bisbenzylisoquinoline classes) (Figure 2), the steroids/triterpenoids (most of which selectively inhibit BchE), the quinolizidines (especially huperzine A), and the indole alkaloids. Here, BCHE is linked to Alzheimer disease.