<prompt> DOC for smoking cessation?AcamprosateVareniclineThalidomideTryptophan  <response>: Ans. B. Varenicline If Bupropion is not an optionAnti-smoking drugs:Bupropion along with Varenicline Nicotine replacement therapy is a USFDA approved first-line agent for pharmacotherapy in smoking cessation.Varenicline:Effective agent for smoking cessation.Synthetic drug with paial agonist action at a4ss2 nicotinic receptors.Has antagonist propeies persisting due to long half-life high receptor affinity.Hence, prevents stimulant effect of nicotine at presynaptic a4ss2 receptors a results in dopamine release. 