What is the primary mechanism of action of varenicline in treating tobacco use disorder?

Varenicline functions primarily as a partial agonist at the alpha4beta2 nicotinic acetylcholine receptor. This action allows it to stimulate these receptors to a certain extent while also blocking nicotine from binding to them. By doing so, varenicline helps to reduce withdrawal symptoms and cravings in individuals quitting smoking, as it mimics the effects of nicotine but does not provide the same level of reinforcement.

This mechanism is particularly beneficial because it alleviates some of the uncomfortable symptoms associated with nicotine withdrawal, making it easier for individuals to stop smoking. It mitigates the reinforcing effects of nicotine, which can help prevent relapse by blunting the reward experienced when the user engages in smoking.

In contrast, other possible mechanisms mentioned are either not accurate representations of how varenicline works or describe unrelated actions.