Piperazine was marketed by Bayer as an anthelmintic in the early 20th century, and was featured in print ads alongside other popular Bayer products at the time, including Heroin. In fact, large number of piperazine compounds have an anthelmintic action. Their mode of action is generally by paralysing parasites, which allows the host body to easily remove or expel the invading organism. The neuromuscular effects are thought to be caused by blocking acetylcholine at the myoneural junction. This action is mediated by its agonist effects upon the inhibitory GABA (γ-aminobutyric acid) receptor. Its selectivity for helminths is because vertebrates only use GABA in the CNS and the GABA receptor of helminths is of a different isoform from that of vertebrates.