Nicotine vs cotinine: why the metabolite lasts ten times longer
Nicotine and cotinine are constantly confused, but they behave very differently in the body. Nicotine clears fast; cotinine, the byproduct your liver makes from it, lasts roughly ten times longer. Understanding the difference explains a lot about how nicotine is measured and why this calculator models one and not the other.
Two molecules, two half-lives
Nicotine itself has a roughly 2-hour half-life, one of the shortest of any commonly used substance. As the liver breaks nicotine down, it produces cotinine, which has a half-life of around 16 to 20 hours. So while nicotine is mostly gone within a day, cotinine from the same exposure persists far longer, accumulating with repeated use.
Why the metabolite lasts longer
Cotinine is more stable and cleared more slowly by the body than its parent compound. That stability is precisely why it is useful as a marker: a molecule that vanished as quickly as nicotine would be a poor indicator of use, whereas cotinine's longer half-life means its concentration reflects exposure over a window of days rather than hours.
What this calculator models
The chart and timeline here show nicotine itself, not cotinine. Nicotine drops to a few percent of its starting dose within about 10 to 14 hours given its 2-hour half-life. Cotinine follows its own much slower curve, so the 'trace amount' point on this chart describes nicotine clearance only and is not a model of the metabolite.
Not medical advice
This content is for informational purposes only. It is not a substitute for advice from a qualified healthcare professional and should not be used to make medication, dosing, or health decisions.