Psychiatry Substance Related and Addictive Disorders 5198e926 The main metabolite of nicotine is A Nornicotine B Carboxynicotine C Cotinine D Nicotine hydroxide High-Yield Explanation Nicotine is metabolized in liver, lung and brain to cotinine by CYP2A6 enzyme. A plasma cotinine levels of >14ng/ml typically indicates smoking.