BDNF and Alzheimer disease: Although there have been several attempts to identify molecules that enhance signaling of neurotrophins—such as natural products, small-molecule peptidomimetics, and receptor agonists—the objective of this review is to focus on the development of novel compounds acting as positive allosteric modulators in clinical development within the field of neurotrophin receptor allostery, with special focus on diseases related to the central nervous system (CNS) such as AD.