Disclosed embodiments concern polycyclic alkaloid compounds and methods for their use and synthesis. Particular embodiments concern polycyclic alkaloids having a fused, six-membered ring, while other embodiments concern polycyclic alkaloids having a fused, five-membered ring. Methods for making the polycyclic alkaloids are disclosed, as well as methods for their use as prophylactics or treatments for certain diseases. Also disclosed are pharmaceutical compositions comprising the polycyclic alkaloids and their use.