How stable is cotinine?
Cotinine has an in vivo half life of about 24 hours. Nicotine’s half-life is about 30 minutes. Timing of sampling relative to the last cigarette smoked may account for some fluctuation of cotinine levels in steady smokers. For smokers with a fairly constant smoking pattern, cotinine levels reach a steady state, varying only by 15%-20% over the course of the day. Levels should be lowest in the morning as there is typically minimal exposure to cigarette smoke overnight. Once a sample is collected, metabolism ceases and cotinine levels should not change; however, saliva or urine left at room temperature for extended periods may experience degradation of cotinine due to bacterial contamination.
