Codeine has a plasma half-life of roughly 2.5 to 3 hours, meaning the drug itself clears your bloodstream within about a day of your last dose. But “out of your system” depends entirely on what you mean and how someone is checking. A standard urine test can pick up codeine or its breakdown products for one to two days, an oral fluid test for about a day, and a hair test for months. These windows differ because each sample type captures a different snapshot of the drug’s journey through your body, and individual biology stretches or shrinks every one of those windows.
How Codeine Moves Through Your Body
After you swallow a codeine tablet, blood levels rise fast. Most people hit peak plasma concentrations within about an hour of an oral dose, though one study measured a slightly later average of 1.2 hours depending on the formulation and the person.1PubMed. Plasma codeine and morphine concentrations after a single oral dose of codeine phosphate An older radioimmunoassay study found peak levels appearing as early as 45 minutes to an hour after oral dosing.2PubMed. Codeine kinetics as determined by radioimmunoassay From that peak onward, the liver gets to work breaking codeine down.
The elimination half-life reported in the literature ranges from about 1.5 hours in one study to about 3.2 hours in another, a spread that reflects differences in study design and population.3PubMed. Pharmacokinetics and metabolism of codeine in humans4PubMed Central. Disposition and metabolism of codeine after single and chronic doses in one poor and seven extensive metabolisers A reasonable working figure for most adults is somewhere around 2.5 to 3 hours. That means after roughly five to six half-lives, or about 12 to 18 hours, the codeine molecule itself has been reduced to negligible levels in plasma. But the story doesn’t end there, because your liver converts codeine into several metabolites, and those metabolites have their own half-lives and their own detection windows.
The Metabolites That Linger Longer
Codeine is what pharmacologists call a prodrug: it is converted in the liver into morphine, which is the metabolite responsible for most of its painkilling effect. This conversion is handled by an enzyme called CYP2D6. Besides morphine, the liver also produces codeine-6-glucuronide, morphine-3-glucuronide, norcodeine, and several other breakdown products, each cleared at a different rate. Codeine-6-glucuronide, for instance, has its own half-life of roughly 2.8 to 3.2 hours.3PubMed. Pharmacokinetics and metabolism of codeine in humans4PubMed Central. Disposition and metabolism of codeine after single and chronic doses in one poor and seven extensive metabolisers Drug tests don’t just look for the parent codeine molecule. Most immunoassay screens detect the whole opiate family, including morphine and its glucuronide conjugates, so even after codeine itself is gone, its downstream products can still trigger a positive result.
The morphine that comes from codeine circulates at much lower concentrations than the parent drug. During steady-state dosing, morphine plasma levels run at only about two to three percent of the codeine concentration.5PubMed. Plasma concentrations of codeine and its metabolite, morphine, after single and repeated oral administration Those small absolute amounts still matter for testing, though, because modern assays are extremely sensitive.
Urine Testing Windows
Urine is by far the most common specimen type in workplace, clinical, and forensic drug testing. After a single dose, codeine and its metabolites are excreted rapidly, with the majority of the drug appearing in urine within the first 24 hours.6Journal of Analytical Toxicology. Forensic Drug Testing for Opiates, III. Urinary Excretion Rates of Morphine and Codeine Following Codeine Administration In practice, a standard urine screen can detect codeine for roughly one to two days after a single therapeutic dose. The exact window depends on the cutoff concentration the lab uses, the dose taken, and individual metabolism.
If you’ve been taking codeine regularly rather than as a one-off, expect the detection window to stretch somewhat. Repeated dosing leads to higher peak plasma codeine concentrations compared with a single dose, and the second dose can produce a higher peak than the first even before true steady state is reached.5PubMed. Plasma concentrations of codeine and its metabolite, morphine, after single and repeated oral administration More drug in the body means more metabolite funneling through the kidneys over a longer period, so chronic users may test positive for an additional day or so beyond the single-dose window.
Oral Fluid and Saliva Tests
Oral fluid testing has become increasingly common, particularly in roadside and workplace settings, because collection is easy and hard to tamper with. The detection window for codeine in oral fluid is roughly comparable to urine but depends heavily on the cutoff the lab applies. Using a very sensitive cutoff of 2.5 micrograms per liter, one study found an average detection time of about 21 hours, which was actually longer than the detection window in plasma.7Clinical Chemistry. Plasma and Oral Fluid Pharmacokinetics and Pharmacodynamics after Oral Codeine Administration With the higher cutoff of 40 micrograms per liter proposed by federal workplace testing guidelines, that detection time shrank to just 7 hours.
A quirk of oral fluid testing is contamination from the dose itself. If you swallowed a liquid codeine preparation, your mouth can harbor extremely high codeine concentrations in the first minutes afterward. One study that gave volunteers a 30-milligram liquid codeine dose found saliva concentrations at 15 minutes ranging from 690 nanograms per milliliter to over 15,000 nanograms per milliliter, far exceeding anything in the blood. After the first couple of hours, though, saliva codeine concentrations fell in step with plasma, just running about three to four times higher in absolute terms.8Journal of Analytical Toxicology. Correlation of Saliva Codeine Concentrations with Plasma Concentrations after Oral Codeine Administration The practical takeaway: if you’re subject to an oral fluid test within an hour or two of swallowing liquid codeine, the result could look wildly elevated for reasons that have nothing to do with how much drug is actually in your system.
Hair Testing
Hair tests operate on an entirely different timescale. Drug molecules get deposited into the hair matrix through the blood supply to the follicle, through sweat, and through sebum. Standard hair testing examines the proximal 3 centimeters of hair (roughly the most recent 3 months of growth) and can detect codeine use long after every trace has left blood and urine.
Codeine has been detected in the proximal 1 centimeter of hair within 30 minutes of a single 120-milligram oral dose, though it did not appear in more distal segments until about 3 weeks later. After a single dose, codeine remained detectable in hair for at least 10 weeks.9PubMed. Codeine disposition in human hair after single and multiple doses Research into the mechanisms of deposition suggests that drugs first enter hair from sweat shortly after dosing, and later from the blood supply to the growing hair cells. Washing the hair removed about half the codeine from specimens collected one to three days after the last dose, but washing was far less effective once the drug had been incorporated into the growing strand over the following weeks.10Journal of Analytical Toxicology. Drug Testing with Alternative Matrices II. Mechanisms of Cocaine and Codeine Deposition in Hair
For someone worried about a hair test specifically, the bottom line is that a single therapeutic course of codeine can leave a detectable mark in your hair for up to about three months, depending on dose size, hair growth rate, and the lab’s sensitivity threshold.
Why Clearance Varies So Much Between People
Quoting a single number for “how long codeine stays in your system” is misleading because individual variation is enormous. Three factors dominate that variation.
The first and often largest factor is your CYP2D6 genetics. The enzyme that converts codeine to morphine comes in dozens of genetic variants, and people are broadly grouped into poor, extensive (normal), and ultrarapid metabolizers. A population pharmacokinetic model estimated that poor metabolizers convert only about 10 percent of a codeine dose into morphine, extensive metabolizers convert about 40 percent, and ultrarapid metabolizers convert roughly 51 percent.11PubMed. CYP2D6 phenotype-specific codeine population pharmacokinetics This has a direct effect on what shows up in your drug test. Ultrarapid metabolizers generate more morphine faster, which means morphine and its conjugates persist in urine at higher concentrations and for a longer window. Poor metabolizers, on the other hand, produce less morphine overall, shifting the balance toward other codeine metabolites. Clinical guidelines explicitly link CYP2D6 genotype to both the safety and efficacy of codeine therapy.12PubMed Central. Clinical Pharmacogenetics Implementation Consortium guidelines for cytochrome P450 2D6 genotype and codeine therapy: 2014 update
Kidney function is the second major variable. Codeine and its metabolites are primarily excreted through the kidneys. In people with chronic kidney disease, those metabolites accumulate rather than being cleared efficiently, and clinical guidance recommends cutting the codeine dose by at least half in these patients, or avoiding it altogether because of the risk of toxic morphine buildup.13PubMed Central. Opioid Prescription in Patients With Chronic Kidney Disease: A Systematic Review of Comparing Safety and Efficacy of Opioid Use in Chronic Kidney Disease Patients If your kidneys are not working well, codeine and its breakdown products will stay detectable in your system longer than the standard estimates.
Liver function is the third factor, for a slightly different reason. The liver is where all of codeine’s transformations happen. In someone with significant liver disease, the conversion to active metabolites can be impaired, which may paradoxically reduce the painkilling effect while still leaving the parent drug circulating longer.14PubMed. Analgesics in patients with hepatic impairment: pharmacology and clinical implications Liver and kidney disease can also interact: the rate and pathways of opioid metabolism are influenced by genetic factors and medical conditions simultaneously.15PubMed Central. Opioid metabolism
Immediate-Release Versus Sustained-Release Formulations
If you’re taking a sustained-release codeine product, the drug enters your bloodstream more slowly, which shifts the timeline. Peak plasma concentrations are delayed, occurring at about 2.3 hours for sustained-release versus 1.1 hours for immediate-release in one head-to-head study. The terminal half-life, however, was essentially the same for both formulations, around 2.6 hours after a single dose.16PubMed. Human pharmacokinetic study of immediate-release (codeine phosphate) and sustained-release (codeine Contin) codeine What this means in practice is that sustained-release codeine doesn’t linger in your system much longer once absorption is complete, but the later onset means the clock starts later. If you take a sustained-release dose, expect the overall detection window to be pushed out by roughly an hour or two compared with an equivalent immediate-release dose.
Codeine and Breastfeeding
For nursing mothers, the question of “how long codeine stays in your system” takes on a different urgency, because the drug and its morphine metabolite both pass into breast milk. Measured milk codeine levels after a dose ranged from about 34 to 314 nanograms per milliliter, with morphine levels from about 2 to 21 nanograms per milliliter. Infant blood samples drawn one to four hours after a feeding showed codeine at very low levels, from undetectable to 4.5 nanograms per milliliter.17PubMed. Codeine and the breastfed neonate
Those numbers are small in absolute terms, but neonates clear morphine far more slowly than adults do. A modeling study found that the mother’s own codeine clearance and the neonate’s limited ability to eliminate morphine are the most critical factors, and that potentially toxic morphine concentrations could build up in a newborn within four days of the mother beginning regular codeine dosing.18PubMed. Risk to the breast-fed neonate from codeine treatment to the mother: a quantitative mechanistic modeling study This risk is especially acute in mothers who are ultrarapid CYP2D6 metabolizers, because they produce more morphine from each codeine dose. Several regulatory agencies have issued warnings or restrictions on codeine use by nursing mothers for exactly this reason.
The Poppy Seed Problem in Drug Testing
One of the more frustrating practical issues around codeine detection has nothing to do with taking codeine at all. Poppy seeds naturally contain both morphine and codeine, and eating food made with them can produce a genuinely positive opiate urine test. This is not an urban legend; it is a well-documented analytical headache.
Forensic scientists have long tried to develop reliable ways to tell whether a positive opiate result came from poppy seeds versus actual codeine or heroin use. One widely cited rule of thumb holds that codeine concentrations above 300 nanograms per milliliter paired with a morphine-to-codeine ratio below 2 point to codeine use rather than poppy seed consumption. But a recent study directly challenged that guideline: after feeding volunteers poppy-seed-containing foods, 18 percent of their urine samples tested positive for codeine while being negative for morphine at the 300 nanogram-per-milliliter cutoff, a pattern that looked exactly like codeine administration.19PubMed. Poppy Seed Consumption May Be Associated with Codeine-Only Urine Drug Test Results Of the samples that tested positive for codeine at all, more than half mimicked the pattern supposedly reserved for drug use.20Journal of Analytical Toxicology. Poppy Seed Consumption May Be Associated with Codeine-Only Urine Drug Test Results
Despite decades of research, no marker or cutoff has been found that can unambiguously separate poppy seed ingestion from opiate use in every case.21PubMed Central. Morphine and Codeine in Oral Fluid after Controlled Poppy Seed Administration If you have an upcoming drug test and recently ate a poppy seed bagel or pastry, the honest truth is that you could test positive for opiates for up to a day or two, and the lab may not be able to tell the difference. Federal workplace testing programs raised their confirmation cutoff for morphine in 2010 partly to reduce false positives from poppy seeds, but the problem has not been eliminated.
Quick Reference by Test Type
Because the detection window varies so much by specimen type, here is a practical summary of approximate windows after a single therapeutic dose in someone with normal kidney and liver function:
- Blood or plasma: Codeine falls below detectable levels within roughly 12 to 18 hours.
- Urine: Codeine and its metabolites are generally detectable for one to two days, occasionally a bit longer with repeated dosing.
- Oral fluid: Around 7 to 21 hours depending on the cutoff concentration the lab applies.7Clinical Chemistry. Plasma and Oral Fluid Pharmacokinetics and Pharmacodynamics after Oral Codeine Administration
- Hair: Detectable for at least 10 weeks and potentially up to about 3 months, even after a single large dose.9PubMed. Codeine disposition in human hair after single and multiple doses
These ranges assume a healthy adult. Impaired kidneys, an ultrarapid CYP2D6 genotype, or chronic high-dose use can push any of these windows outward. Conversely, a poor metabolizer with healthy organs may clear the drug and its metabolites a bit faster than average for certain assays, because less morphine is being generated in the first place.
Drug Interactions That Slow Clearance
Because codeine depends on CYP2D6 for its primary metabolic pathway, anything that inhibits that enzyme can change how quickly codeine and its products leave your body. Common CYP2D6 inhibitors include certain antidepressants like fluoxetine and paroxetine, the antihistamine diphenhydramine, and the heart medication quinidine. Taking one of these drugs alongside codeine effectively makes you behave like a poor metabolizer regardless of your genetics, reducing morphine formation while potentially allowing the parent drug to circulate longer. On the flip side, some medications can induce metabolic enzymes and speed codeine’s breakdown, though this is less common and less clinically significant for CYP2D6 specifically.
The practical result for drug testing is that co-medications can shift both the metabolite profile and the total detection window in ways that are hard to predict without knowing your full medication list. If you are on an interacting drug and facing a test, expect your results to look a bit different from textbook timelines.