(R)-Praziquantel ((R)-PZQ) is a G-protein-coupled receptor ligand. (R)-Praziquantel modulation of serotoninergic signaling occurs over a concentration range sufficient to regulate vascular tone of the mesenteric blood vessels where the adult parasites reside within their host. The important anthelmintic is supported by a broad, cross species polypharmacology with (R)-Praziquantel modulating signaling events in both host and parasite.