Which major nicotine metabolite is commonly used as a biomarker of exposure in biological samples?

• A. Cotinine
• B. Nicotine
• C. Nornicotine
• D. Anabasine

Answer: (A)

Cotinine is the major nicotine metabolite used as a biomarker of exposure because it stays in the body much longer than nicotine itself. When nicotine is absorbed, the liver converts most of it to cotinine, mainly via the enzyme CYP2A6. Cotinine has a longer half-life—roughly a day or more depending on the person—so it remains detectable in blood, saliva, or urine even after nicotine levels have fallen. This stability makes cotinine a reliable indicator of tobacco exposure over the recent past, which is why it’s widely used in research and clinical assessments.

Other nicotine metabolites do exist, but they’re not as useful for gauging overall exposure. For example, nornicotine appears in smaller amounts and provides less consistent information, while anabasine can help distinguish exposure to tobacco products from nicotine replacement therapies in some contexts but isn’t the general biomarker of exposure.