Piperazinyl oxoalkyl tetrahydroisoquinolines and related analogues of the Formula: are provided, in which variables are as described herein. Such compounds may be used to modulate ligand binding to histamine H3 receptors in vivo or in vitro, and are particularly useful in the treatment of a variety of central nervous system (CNS) and other disorders in humans, domesticated companion animals and livestock animals. Compounds provided herein may be administered alone or in combination with one or more other CNS agents to potentiate the effects of the other CNS agent(s). Pharmaceutical compositions and methods for treating such disorders are provided, as are methods for using such ligands for detecting histamine H3 receptors (e.g., receptor localization studies).