Varenicline(CP 526555) is highly selective and blocks more potently to α4β2 receptors than to other common nicotinic receptors (>500-fold α3β4, >3,500-fold α7, >20,000-fold α1βγδ), or to non-nicotinic receptors and transporters (>2,000-fold). Varenicline also acts as an agonist of 5-HT3 serotonine receptors.