Vaping products contain nicotine, but they do not contain cotinine. Cotinine is a chemical compound created through a metabolic process after nicotine has been absorbed. When someone vapes an e-liquid containing nicotine, they introduce the parent compound into their system, which the body then processes into the metabolite cotinine.
Understanding Cotinine: Nicotine’s Metabolite
Cotinine is the primary breakdown product of nicotine. This chemical change primarily takes place in the liver, where the cytochrome P450 enzyme CYP2A6 converts approximately 70% to 80% of absorbed nicotine into cotinine. This metabolic process explains why cotinine is present in the body after using a nicotine-containing vape, even though it was not an ingredient in the e-liquid itself.
Cotinine is a valuable biomarker for nicotine exposure. Nicotine itself has a relatively short half-life—the time it takes for half of the substance to be eliminated—often lasting only a few hours. Cotinine, however, has a much longer half-life, typically ranging from 15 to 20 hours, and sometimes extending up to 40 hours. This extended presence makes cotinine a reliable indicator of recent nicotine use, surpassing the utility of testing for nicotine alone.
Nicotine Content in E-Liquids
Manufacturers use two main forms of nicotine in vaping products: freebase nicotine and nicotine salts. Freebase nicotine is the purest form, which is alkaline and often results in a harsh throat sensation at higher concentrations. E-liquids using freebase nicotine are commonly sold in lower concentrations, typically ranging from 3 to 12 milligrams per milliliter (mg/mL).
Nicotine salts are created by adding an organic acid, such as benzoic acid, to the freebase nicotine. This chemical modification lowers the pH, which reduces the harshness and allows for a much smoother inhalation experience, even at very high strengths. Nicotine salt e-liquids are therefore often available in concentrations ranging from 20 to 50 mg/mL, delivering a more rapid and intense nicotine dose. It is also possible to purchase e-liquids that contain zero nicotine, meaning no cotinine would be produced upon use.
Factors Affecting Cotinine Detection
Cotinine’s longer half-life makes it the primary chemical tested to determine recent nicotine exposure. A substance is considered eliminated from the body after four to five half-lives, meaning cotinine can remain detectable for several days after the last use. Testing methods rely on different biological samples, each offering a specific detection window.
Urine testing is the most common method and can detect cotinine for up to seven days, depending on the concentration cutoff used by the laboratory. Saliva and blood samples also show cotinine, but their detection window is often shorter than urine. The amount of cotinine measured is directly proportional to the frequency of vaping and the concentration of nicotine used, with heavy use leading to higher and longer-lasting cotinine levels.
Individual metabolic rates influence how long cotinine remains detectable. The efficiency of the CYP2A6 enzyme, which is influenced by genetics, varies significantly among people. Individuals who are “slow metabolizers” retain cotinine for a longer period than “fast metabolizers,” even with the same level of nicotine intake.