Varenicline (CP 526555) is a potent partial agonist for α4β2 nicotinic acetylcholine receptor (nAChR) with an EC50 value of 2.3 μM. Varenicline is a full agonist for α3β4 and α7 nAChRs with EC50 values of 55 μM and 18 μM, respectively. Varenicline is a nicotinic ligand based on the structure of cytosine, and has the potential for smoking cessation treatment.