What Is Cotinine? The Nicotine Test Explained

Quick answer: Cotinine is what nicotine becomes in your body: the liver converts about 70–80% of nicotine to cotinine, mainly through the enzyme CYP2A6. Its half-life averages about 16 hours, against about 2 hours for nicotine, which is why most "nicotine tests" actually measure cotinine. The current optimal blood cut-off to separate smokers from non-smokers in the US is 3 ng/mL.

If you've had a blood or urine test for insurance, surgery or a workplace programme, the "nicotine test" was probably measuring cotinine. Here's what it is, how long it lasts, and what a cotinine test can and cannot tell.

From Nicotine to Cotinine: The Conversion

Nicotine reaches the liver, where — according to the standard pharmacology review — about 70–80% is converted to cotinine, mainly by the enzyme CYP2A6. Cotinine is then broken down further, mostly into 3′-hydroxycotinine.

Key differences:

Nicotine half-life: averages about 2 hours — see nicotine half-life explained
Cotinine half-life: about 16 hours on average (16–18 hours in the review's table)
Nicotine is the addictive drug; cotinine is its breakdown product and a far better marker, because it stays in the blood long enough to measure and its level swings much less between cigarettes

What Cotinine Tests Measure

Cotinine can be measured in blood, urine, saliva, hair or nails.

Blood and saliva: closely related; a snapshot of the last few days
Urine: easy to collect; concentrations run higher than in blood, so cut-offs are higher too
Hair and nails: a record of exposure over months; the review calls them promising markers of long-term exposure

How long each stays positive depends on how much you smoked, how fast you clear cotinine, and the lab's cut-off. Nobody can honestly give you a fixed number of days — see how long nicotine stays in your body for the arithmetic.

Interpreting Cotinine Levels

The review gives these reference points:

Groups of cigarette smokers average about 250–300 ng/mL of cotinine in the blood; some tobacco users reach 900
The current optimal blood (plasma) cut-off to distinguish smokers from non-smokers in the general US population is 3 ng/mL
An older cut-off, still widely seen, was 15 ng/mL in blood or saliva and 50 ng/mL in urine; the review says the cut-off came down because there is now less secondhand smoke about and more light or occasional smoking

Labs vary, so the cut-off on your report is the one that matters. We don't print a finer table of levels by smoker type, because we could not trace one to a source.

Why Heavier Smokers Test Positive Longer

Heavier smokers start higher, so their cotinine needs more half-lives to fall below the same cut-off. Clearance also varies between people: slow CYP2A6 metabolisers, people over 65 and people with severe kidney disease clear nicotine more slowly, and smoking menthol cigarettes slows the conversion of nicotine to cotinine, the review says.

Cotinine and Nicotine Replacement Products

NRT products (patches, gum, lozenges, inhalators) and e-cigarettes all deliver nicotine, which becomes cotinine. A cotinine test will be positive, whatever the source.

That matters for insurance tests and pre-surgery screening, where some programmes count any nicotine as tobacco use. But other tests can separate tobacco from NRT: the minor tobacco alkaloids anatabine and anabasine are found in tobacco but not in nicotine medicines, and the review notes this approach has been used in clinical trials to confirm abstinence from tobacco in people using NRT. The tobacco-specific marker NNAL likewise comes only from tobacco. If you're on NRT and facing a test, ask whether one of these is available.

Cotinine as a Research Biomarker

In research, cotinine is the standard way to check what people say about their smoking, because self-report can be wrong.

Researchers also use the nicotine metabolite ratio (NMR) — 3-hydroxycotinine to cotinine — as a measure of how fast your CYP2A6 enzyme works. A randomised trial found that normal metabolisers did better on varenicline than on the patch, while slow metabolisers did about as well on the patch. It's not yet a routine clinic test, but it shows why the same product doesn't suit everyone — see patches versus gum.

After Quitting: How Fast Cotinine Falls

Once you stop all nicotine:

Cotinine halves roughly every 16 hours on average
Falling from a typical smoker's 250–300 ng/mL to the 3 ng/mL cut-off takes about 6–7 half-lives — roughly four to five days, on average figures
Heavier smokers, slow metabolisers and stricter cut-offs push that out; light smokers and higher cut-offs bring it in

Some people use home urine test strips to watch the result turn negative. Check which cut-off the strip uses.

Sources

Benowitz NL, Hukkanen J, Jacob P. "Nicotine chemistry, metabolism, kinetics and biomarkers." Handbook of Experimental Pharmacology, 2009. PMC
Benowitz NL. "Cotinine as a biomarker of environmental tobacco smoke exposure." Epidemiologic Reviews, 1996. PubMed
Hukkanen J, Jacob P, Benowitz NL. "Metabolism and disposition kinetics of nicotine." Pharmacological Reviews, 2005. PubMed
Dempsey D et al. "Nicotine metabolite ratio as an index of cytochrome P450 2A6 metabolic activity." Clinical Pharmacology & Therapeutics, 2004. PubMed
Lerman C et al. "Use of the nicotine metabolite ratio as a genetically informed biomarker of response to nicotine patch or varenicline for smoking cessation." Lancet Respiratory Medicine, 2015. PubMed

Frequently Asked Questions

Will NRT patches or gums fail a cotinine test?

Yes — a cotinine test detects nicotine's breakdown product whatever the source, so patches, gum, lozenges and e-cigarettes all produce a positive result. Tests for anatabine, anabasine or NNAL can show you have stopped tobacco while using NRT; ask whether one is available.

How can I pass a cotinine test quickly?

There is no reliable way to speed up cotinine clearance. Products sold as "nicotine detox" have no evidence behind them. Time without any nicotine is the only method.

Does secondhand smoke affect cotinine levels?

Yes, but usually far less than smoking. People heavily exposed to secondhand smoke can carry measurable cotinine, and a low cut-off such as 3 ng/mL is closer to that range, so borderline results may deserve a follow-up.

Can cotinine testing distinguish cigarettes from vaping?

No. Cigarettes, vapes and NRT all produce cotinine. Tobacco-specific markers such as anatabine, anabasine and NNAL can show tobacco use, though how they behave in vapers is less studied.