This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Drug used for cessation of smoking ? 
Select and explain. 
A. Theophylline, B. Biclutamide, C. Salmeterol, D. Varenicline
D: Varenicline
Answer: D: Varenicline 
Explanation: Ans. is 'd' i.e., Varenicline Varenicilline is a direct acting nicotine agonist with selective action on a4 P2isoform of N. receptors. It is an antismoking drug.