Varenicline Hydrochloride (C₁₃H₁₃N₃·HCl, CAS: 249296-44-4) is a synthetic specialty chemical primarily used as a pharmaceutical active ingredient to aid in smoking cessation. It acts as a partial agonist at nicotinic acetylcholine receptors in the brain, reducing both the pleasurable effects of smoking and the withdrawal symptoms associated with quitting. This dual action helps individuals gradually decrease their dependence on nicotine. It is often prescribed as part of a comprehensive quit-smoking program, which may include counseling and behavioral support. The treatment is typically initiated one week before the planned quit date to allow the medication to build up in the system. It is also utilized in laboratory and research settings as a reference standard. It is important to follow the prescribed dosage and duration to maximize effectiveness and minimize potential side effects.