Cotinine

Cotinine is an alkaloid found in tobacco and is also a metabolite of nicotine. The word "cotinine" is an anagram of "nicotine". Cotinine is used as a biomarker for exposure to tobacco smoke and has also been sold as an antidepressant under the brand name Scotine.

Similarly to nicotine, cotinine binds to, activates, and desensitizes neuronal nicotinic acetylcholine receptors, though at much lower potency in comparison. It has demonstrated nootropic and antipsychotic-like effects in scientific research.

Measure of tobacco smoke exposure
Cotinine has an in vivo half-life of approximately 20 hours, and is typically detectable for several days (up to one week) after the use of tobacco. The level of cotinine in the blood is proportionate to the amount of exposure to tobacco smoke, so it is a valuable indicator of tobacco smoke exposure, including secondary (passive) smoke. People who smoke menthol cigarettes may retain cotinine in the blood for a longer period because menthol can compete with enzymatic metabolism of cotinine. Genetic encoding of liver enzymes may also play a role, as people of African descent routinely register higher blood cotinine levels than Caucasians. Several variable factors (such as menthol cigarette preference and puff size) suggest that the explanation for this difference may be more complex than gender or race.

Cotinine levels <10 ng/mL are considered to be consistent with no active smoking. Values of 10 ng/mL to 100 ng/mL are associated with light smoking or moderate passive exposure, and levels above 300 ng/mL are seen in heavy smokers - more than 20 cigarettes a day. In urine, values between 11 ng/mL and 30 ng/mL may be associated with light smoking or passive exposure, and levels in active smokers typically reach 500 ng/mL or more. Cotinine assays provide an objective quantitative measure that is more reliable than smoking histories or counting the number of cigarettes smoked per day. Cotinine also permits the measurement of exposure to second-hand smoke (passive smoking).

Drug tests can detect cotinine in the blood, urine, or saliva.