Compounds of formula (I) 1 wherein R.sub.1 or R.sub.2 is a tricyclic or bicyclic ring, each of which contains at least two heteroatoms, and R.sub.1, R.sub.2, R.sub.3, R.sub.3a, R.sub.3b, R.sub.4, R.sub.5, L, X, X', Y, Y', Z, and Z' are as defined herein, are useful in treating conditions or disorders prevented by or ameliorated by histamine-3 receptor ligands. Also disclosed are pharmaceutical compositions comprising the histamine-3 receptor ligands, methods for using such compounds and compositions, and a process for preparing compounds within the scope of formula (I).