A nicotinic agonist is a drug that mimics the action of acetylcholine (ACh) at nicotinic acetylcholine receptors (nAChRs). The nAChR is named for its affinity for nicotine.
Examples include nicotine (by definition), acetylcholine (the endogenous agonist of nAChRs), choline, epibatidine, lobeline, varenicline and cytisine.
Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or released from the mouth, as is done with pipes and cigars. The practice is believed to have begun as early as 5000–3000 BC in Mesoamerica and South America. Tobacco was introduced to Eurasia in the late 17th century by European colonists, where it followed common trade routes. The practice encountered criticism from its first import into the Western world onward but embedded itself in certain strata of several societies before becoming widespread upon the introduction of automated cigarette-rolling apparatus.
Smoking is the most common method of consuming tobacco, and tobacco is the most common substance smoked. The agricultural product is often mixed with additives and then combusted. The resulting smoke, which contains various active substances, the most significant of which is the addictive psychostimulant drug nicotine (a compound naturally found in tobacco), is absorbed through the alveoli in the lungs or the oral mucosa. Many substances in cigarette smoke, chiefly nicotine, trigger chemical reactions in nerve endings, which heighten heart rate, alertness and reaction time, among other things. Dopamine and endorphins are released, which are often associated with pleasure, leading to addiction.