This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Substance Related and Addictive Disorders, Subject name: Psychiatry
The main metabolite of nicotine is 
Select and explain. 
A. Nornicotine, B. Carboxynicotine, C. Cotinine, D. Nicotine hydroxide
C: Cotinine
Answer: C: Cotinine 
Explanation: Nicotine is metabolized in liver, lung and brain to cotinine by CYP2A6 enzyme. A plasma cotinine levels of >14ng/ml typically indicates smoking.