Which smoking cessation medication primarily acts as a partial agonist at nicotinic receptors?

Varenicline is a smoking cessation medication that primarily acts as a partial agonist at the alpha-4 beta-2 nicotinic acetylcholine receptors in the brain. This mechanism helps to reduce cravings and withdrawal symptoms associated with quitting smoking. By partially stimulating these receptors, varenicline mimics nicotine's effects, but with less intensity, which helps ease the transition away from nicotine dependence.

At the same time, because it is a partial agonist, varenicline also blocks nicotine from binding to these receptors. This blockade further diminishes the rewarding effects of nicotine if a person relapses, making it less appealing to smoke again. This dual action effectively helps individuals to become nicotine-free while managing cravings and withdrawal, thereby contributing to its success as a smoking cessation aid.

The other medications listed do not have this specific mechanism of action. Bupropion serves as a norepinephrine-dopamine reuptake inhibitor, and nicotine replacement therapies (NRT) supply nicotine to the user directly without affecting the receptors in the same way that varenicline does. Nortriptyline is a tricyclic antidepressant that has shown some effectiveness in helping with smoking cessation but does not act on the nicotinic receptors.