cotinine

A chemical substance formed by the breakdown of nicotine in the body. Nicotine is an addictive, harmful chemical found in tobacco and tobacco products, including cigarettes and chewing tobacco. Exposure to nicotine can be measured by checking the amount of cotinine in the blood, urine, or saliva in smokers and in nonsmokers exposed to secondhand smoke. Cotinine stays in the body longer than nicotine and is used to help monitor tobacco use and the use of nicotine replacement therapy in people trying to stop smoking.